
i 



LIBRARY OF CONGRESS. 
"5" 






UNITED STATES OF AMERICA, 




MUSCLES. 



An 



Elementary Physiology 



WITH SPECIAL REFERENCE TO 



Hygiene, Alcohol and Narcotics 

S" BY 

Richard J. Dunglison, A.M., M.D. 

Author of "A New School Physiology," " Handbook of Diagnosis, Therapeutics 

and dletitics," editor of dunglison's "medical dictionary," 

"History of Medicine," Etc. Secretary of 

the American Academy of 

Medicine 







GHICAGO NEW YORK 

The Werner Company 



^ 






Copyright, 1885, by PORTER & COATES 
Copyright, 1894, by The WERNER Go.MPANY 



Ele'nt't Phys. 



PREFACE. 



The importance of instilling into the youthful mind, 
in its very earliest search after knowledge, a wholesome 
sense of the terrible consequences of any form of indul- 
gence in the use of alcohol, tobacco, and narcotics seems 
to be universally appreciated at the present day. 

The child, when once taught the formation of its own 
body, and how necessary it is to observe all the laws of 
health, cannot fail to regard the use of these poisons, and 
the vicious habits resulting from them, as fertile sources 
of disease, and will be able to convince its parents and 
friends, by its knowledge of Physiology, of the folly 
and wickedness of indulgence in such intoxicating 
agents. By their injurious influences these undermine 
the mental and physical health of individuals and com- 
munities, and lead by paths of crime and suffering to 
lives of poverty and wretchedness. 

The author has endeavored in these pages to present 
as full a statement as is possible in an elementary work 
of all the main facts in Physiology which may interest 



4 PREFACE. 

and instruct the young, and at the same time, interwoven 
with each subject, to make prominent mention of the 
action of alcohol, tobacco, and narcotics generally, be- 
lieving that the study of Physiology will be prosecuted 
with increased vigor when taught from the standpoint 
of temperance and morality. The physiological facts 
and the general laws of hygiene, or the preservation of 
health, herein offered, will, it is hoped, lead naturally 
and instinctively to a just appreciation of such viola- 
tions of the laws of health as are caused by the use of 
alcohol and other narcotics. The author believes that 
the correct method of teaching these subjects is by 
simultaneous instruction in the great principles of 
Physiology, Hygiene, and Temperance. 

As the author has made it a rule to explain and divide 
for proper pronunciation all the technical terms as they 
occur in the text, it has not been deemed necessary to 
add a glossary at the end of the work. 

RICHARD J. DUNGLISON. 



CONTENTS. 



INTRODUCTORY. 

PAGE 

Physiology 9 

Animals and Vegetables 11 

Anatomy ; Divisions of the Human Body 12 

The Skeleton 14 

THE BONES AND JOINTS. 

The Bones ; Bones of the Trunk 18 

Bones of the Lower Extremities ; Bones of the Upper Extremities . . 22 

The Joints 23 

Hygiene of the Bones 29 

Effect of Alcohol on the Bones 30 

THE MUSCLES. 

The Muscles 32 

Tendons 35 

Movements 37 

Hygiene of the Muscles 38 

Action of Alcohol and Tobacco on the Muscles 41 

DIGESTION. 

Food of Man 44 

Gums, Starches, and Sugars 46 

Albuminous Substances ; Fats 47 

Nitrogen 48 

Animal Food 50 

Milk 51 

Eggs 52 

Vegetable Food; Bread 53 

Cooking; Fruit 54 

Drinks 55 

Alcoholic Drinks 56 

Effect of Tobacco and Opium on Digestion 58 

Tea and Coffee 59 

Quantity of Food to be Taken 60 

Hunger and Thirst 62 

Hints about Eating 63 

Organs of Digestion 64 

The Mouth ; The Teeth 65 

5 



6 CONTENTS. 

PAGE 

The Tongue , 70 

The Salivary Glands 71 

Swallowing the Food 72 

The Process of Digestion 75 

Digestion in the Stomach and Intestines 76 

Stomachs of Other Animals 80 

Action of the Stomach 84 

Changes in the Food in Digestion 85 

Digestibility of Food 87 

Digestion in the Intestines 88 

Intestines of Other Animals ; Intestinal Juices 90 

How the Food is Absorbed 93 

Lymphatics 95 

RESPIRATION. 

Why we Breathe 100 

The Chest and its Contents 101 

The Lungs 102 

The Act of Breathing 104 

Number of Respirations; Sounds of the Chest 106 

Capacity of the Lungs; The Air-Cells; The Air we Breathe .... 107 

Some Ordinary Breathing Acts 108 

How Breathing is sometimes Interfered with 109 

Hygiene of the Respiration HO 

Action of Alcohol on the Respiration 112 

Action of Tobacco on the Respiration; Respiration in Other Animals . 113 

Respiration in the Vegetable 116 

CIRCULATION. 

The Circulation Defined 117 

The Heart 118 

Cavities of the Heart 119 

The Greater and Lesser Circulations 120 

Valves of the Heart; Movements of the Heart 122 

Sounds of the Heart ; Course of the Circulation ; The Pulse .... 123 

The Heart's Work 124 

The Quantity of Blood; The Arteries 125 

Pulse-Writing 126 

The Veins 127 

Valves of the Veins; The Capillaries; Circulation in Other Animals . 128 

The Blood Itself; The Blood-Globules 130 

White Corpuscles 131 

Coagulation of the Blood 133 

Hygiene of the Circulation 134 



CONTENTS. 7 

PAGE 

Action of Alcohol on the Heart and the Circulation 134 

Action of Tobacco on the Circulation 136 

The Effect of Narcotics j Mortality from Alcohol 137 

Materials Separated from the Blood 137 

Glands; Secreting Structures 138 

ANIMAL HEAT. 

Temperature of Animals 140 

Temperature of Different Organs ; Hygiene of Animal Heat .... 141 

Action of Alcohol on the Temperature 143 

Effect of Tobacco on the Temperature 144 

THE NERVOUS SYSTEM. 

Peculiar to Animals Alone; Divisions of the Nervous System; Ner- 
vous Matter 145 

The Cerebro-Spinal System , 147 

The Brain 148 

Weight and Size of the Brain 149 

The Brain Proper 150 

Cerebellum ; Spinal Cord ; The Nerves 151 

The Nerves in Pairs 152 

Cranial Nerves 153 

Spinal Nerves 154 

Great Sympathetic Nerve 155 

Functions of the Medulla Oblongata ; Functions of the Cerebellum ; 

Functions of the Cerebrum, or Brain Proper 158 

Sleep ; The Nervous System of Animals 159 

Hygiene of the Nervous System ; Action of Alcohol upon the Nervous 

System 160 

Action of Opium upon the Nervous System 162 

Action of Chloral Hydrate, etc. ; Action of Tobacco 163 

THE SENSES. 

Their Objects, etc . 165 

Taste. 

The Organ of Taste 165 

Conditions of Taste 166 

Nerves to the Tongue; Organ of Taste in Other Animals .... 167 

Smell. 

The Organ of Smell; The Nerve of Smell 168 

Odors; How Smell is Effected; Sense of Smell in Animals .... 169 



8 CONTEXTS. 

PAGE 

Touch. 

The Organ of Touch 170 

The Skin; Sweat-Glands 171 

Sebaceous or Fat- Glands; Hair 172 

Color of the Skin; The Hand; The Sensation of Touch . .... 173 

Sense of Touch in Other Animals; Hygiene of the Skin 174 

Vision. 

The Organ of Vision 176 

Protection of the Eye ; The Tears 177 

The Orbits; The Eyelids ; The Eyelashes 178 

Transparent Parts of the Eye ; Coverings of the Eye 179 

Light; The Course taken by the Kays of Light 180 

The Image on the Retina; Ear Sight and Short Sight 181 

Impression on the Retina 182 

Perception of Colors 183 

Vision in Other Animals 184 

Hygiene of the Eyes 185 

Effect of Alcohol and Tobacco on Vision 186 

Hearing. 

The Organ of Hearing 188 

How Sound is Heard 189 

Sound; The Sense of Hearing in Other Animals; Hygiene of the 

Hearing 191 

Effect of Alcohol and Tobacco on the Hearing 192 

VOICE. 

The Organ of Voice ; The Larynx ; The Vocal Cords 194 

Muscles of the Larynx ; How Voice is Produced 195 

Quality of Voice 196 

The Singing and the Speaking Voice 197 

The Formation of Language ; The Voice and the Hearing ; Hygiene 

of the Voice 198 

Effect of Alcohol and Tobacco on the Voice 200 

The Voices of Animals 200 

I^DEX . , . . . . f 203 



ELEMENTARY 
PHYSIOLOGY AND HYGIENE. 



Physiology. — When we look at the world around us, 
we see that it is made up of bodies of various kinds, 
some of which have life and grow from day to day and 
from year to year, and then die, and others which have 
no life or movement, such as the stones in the street or 
the bricks of the houses. Those which have life, such 
as the people, the trees and plants, are called animals or 
vegetables. When we study physiology, we do not con- 
cern ourselves with the lifeless things around us or with 
living vegetables or plants, but we study the life of 
animals only. Man is the most perfect animal of all ; 
and when we study his physiology we do so that we may 
learn how he breathes, how the blood passes through his 
body to keep him in good health, and what he must eat 
to give him strength and prolong life ; and we must also 
learn something about his brain, and how it is that he 
can move about from place to place at his own will. We 
must also study his eye and his ear, and try to learn in 
what way they are formed so that he can see and hear 
so well. 

The word Physiology means a study of nature, or of 

9 



10 ELEMENTARY PHYSIOLOGY. 

the living things around us. Vegetable Physiology is a 
study of the life of plants only. 

In that kind of ancient story, which is sometimes 
called mythology, there were said to be gods and god- 
desses whose business it was to look after the good and 
bad things of this world. Health, one of the best of 
Nature's gifts, was said to be presided over by the God- 
dess of Health, and the name Hyge'ia was given to her, 
from a Greek word meaning health. So when writers or 
others now speak of the rules for preserving health they 
give the name Hy'giene to this subject. 

There cannot be any higher study of nature than that 
which we have of our own bodies, for we can there 
see how wonderful a work of creation we are, and how 
all our organs act together to keep us alive and in good 
health. We can learn much about ourselves by merely 
examining our bodies ; we can feel our hearts beat, can 
study our own breathing, know that our joints are mov- 
able, and learn what hunger and appetite are, and so be 
able to understand much that is taught us in the study 
of physiology. If we understand all this, w r e will soon 
learn that we should take the best of care of our bodies, 
so that we may enjoy good health and avoid all such 
things as will cause sickness. 

Some writers speak of the human body as a machine, 
and they describe it just as they would a clock or a 
steam-engine, telling what each part is used for and how 
it is made, and how all the different parts of the machine 
work together. This is the best way of studying our 
own bodies, and of learning the uses of all the different 



PHYSIOLOGY. 1 1 

parts, which are so closely connected that if anything 
should get out of order in one portion of the body all 
the other portions may suffer also. 

Animals and Vegetables. — Before studying physiology 
it would be well to notice in what way the bodies which 
have life, such as animals and vegetables, differ from 
one another. They are all made up of parts, or organs, 
as they have been called. An animal has, for example, 
eyes, ears, and stomach, which are its organs ; while a 
plant or a tree has leaves, flowers, bark, etc., which are 
the organs of the plant. A bird has wings, which are 
its organs with which to fly. Each of these organs, in 
the plant as well as in the animal, has certain w T ork to do 
to help keep it alive and to enable it to grow. If any 
of these organs be injured, the animal or the plant may 
droop and die. A mineral, having no organs, cannot 
have life, and cannot grow, as animals or plants do. A 
child may grow to be a man, and a seed, planted in the 
ground, may become a large bush or a tree, but a stone 
will never get to be of larger size, except by the addition 
of other things to it, such as particles of dust or dirt. 
The parts of a living body differ from one another : the 
leaves are not like the flower ; the bones are not like the 
flesh ; but any part of a stone is like any other part. 

When we speak of animals, we of course include man, 
and all the beasts, birds, fishes, insects, or reptiles which 
we see or read about. It is not necessary that we should 
know the physiology of all these animals before w r e can 
understand that of man, but it is well for us to learn 
how they breathe and move and live, and then we can 



12 ELEMENTARY PHYSIOLOGY. 

know how much God has done for man in placing him 
so high above all the other animals and in giving him 
such perfect organs for carrying on life. 

Anatomy. — When we study physiology, we study the 
uses of the different organs of the body, but we must 
also understand their form and what they are made of, 
as well as their uses; and we have therefore to learn 
something of their Anat'omy, as it is called, for anatomy 
is that branch of study which describes the appearance 
and structure of the different parts of the body. When 
we say that the teeth are so many in number, and that 
they are arranged in the mouth in a certain way, and 
that the jaw has spaces in it in which the teeth fit, we 
are speaking of the anatomy of the teeth • but when we 
say that our teeth are used to break up the food after 
it is placed in the mouth, and that some of the teeth 
crush it while other teeth cut it, we speak of the 
physiology of the teeth. 

Animals have the power of moving from place to 
place of their own will. Vegetables or plants have not 
this power, for they are fixed to the earth, and must get 
their food from the ground and from the moisture con- 
tained in it. A vegetable cannot feel, and has no brain 
to guide its movements as an animal has. Some of the 
lowest animals have very little sense or feeling or power 
to move about. 

Divisions of the Human Body. — When we look at a 
child or a man, we see that the body of each can be 
divided into four parts — a head, a body or trunk, upper 
extremities, and lower extremities. The whole body is 



PHYSIOLOGY. 13 

covered with a very delicate organ called the Skin, which 
protects it from injury, and with the fat beneath it serves 
as a cushion for the parts which it covers. If we notice 
any other animals, such as the cat or dog, w r e will see 
that they are covered with fur or hair, which have the 
same wise purpose. Birds have feathers to protect them 
from the air or from cold ; the elephant has a thick hide ; 
the tortoise and oyster have hard shells ; fish have scales, 
— all with the object of keeping their other organs from 
being injured. So also we find in man such a protection 
as nails at the ends of the fingers, and hair on the head. 
If such was not the case, the ends of the fingers w r ould 
be too tender for the different uses to which they are put 
in touching and handling objects, and if the head were 
not covered by a thick growth of hair, it would be ex- 
posed to the full force of blows or to the effect of the 
cold air or of the hot sun. 

The Head is composed of a front part called the Face, 
and a back part called the Skull. In the face are the 
eyes, nose, and mouth, the cheeks, chin, and forehead. 
The Skull is usually covered with hair. It is a col- 
lection of eight bones of various sizes, fitted tightly to- 
gether, so as to form a cavity in which is placed the 
brain (Fig. 1). The Face is made up of fourteen sep- 
arate bones united together and firmly fastened to the 
skull, which is behind it. The lower jaw is the only 
one of the bones of the face that is movable, and this is 
made so in order that the mouth may be opened and 
closed. The bones of the face are hollowed out in some 
parts and made to stand out in other places, so as to 



14 



ELEMENTARY PHYSIOLOGY. 



form sockets for the eyes, the bridge of the nose, and 
other points which give shape to the face. 




I'ig. i. — Bones of the Skull, separated from one another. 

The Body or Trunk is divided into the neck, chest, 
and abdo'men, which most persons wrongly call the 
stomach. The Upper Extremities include the shoulders, 
arms, hands, and fingers. The Lower Extremities in- 
clude the thighs, legs, feet, and toes. We shall learn the 
uses of these parts when we come to study the physiology 
and uses of all these organs. 

The Skeleton. — When w T e study the human body to 
see of what organs it is made up, w T e find a great variety, 
and these are so placed inside the body that they are not 
likely to be injured. The framework of the body is 
called the Skeleton (Fig. 2), and it is made up of more 



Spinal column. 
Collar-bone, 

Shoulder-blade. — ■§{ 
Breast-bone. — J 

Ribs. 
False ribs.—j 



— Humerus. 




Bones of 

ankle 
and foot. 



Ftg. 2. — The Skeleton. 



16 ELEMENTARY PHYSIOLOGY. 

than two hundred bones. These are so arranged as to 
allow of all parts of the body moving easily, and the 
bones also give a firm and hard base for the various por- 
tions of the body to rest upon. It will be seen from 
Fig. 2 that these bones are of a great variety of shape 
and size, and the reader will be able to feel many of them 
on his own person directly under the skin, as in the skull 
and at the elbow, hands, knee, etc. The names of the 
largest of these bones are given in the figure, but it is 
not necessary for the youngest readers to commit them to 
memory. 

The skeleton has the skull at the top, and connected 
with it is the spine, or spinal column, w r hich is a long 
row of bones, the sharp points of many of w T hich can be 
felt along the back. The bones of the upper and lower 
extremities (Fig. 2) are of different sizes, and are so 
arranged that the various portions of the limbs can be 
readily moved. 

The bones are all covered with 3£uscles, which are 
masses of fleshy matter, the use of which is to give 
motion to the parts which they cover or to which they 
are fastened. The bones and muscles form cavities or 
spaces, which are closed and air-tight, and in these cav- 
ities the heart and lungs and other organs intended for 
purposes of life are packed away. The bones and mus- 
cles of the chest, for instance, form a cavity in w T hich the 
heart and lungs are placed, and the bones and muscles 
of the abdomen are so arranged that a large space is left, 
w r hich is filled up chiefly by the stomach and bowels. 
In the chest — one of these great cavities or spaces — 



PHYSIOLOGY. 17 

breathing: is mainlv effected and the blood is sent out 
from the heart. In the cavity of the abdomen the food 
is acted upon and absorbed in the stomach and intestines. 
In the cavity of the skull the brain is stored away, and 
with it the organs of sight, smell, taste, and hearing. 

Besides the bones and muscles and other organs just 
referred to, there are Blood-vessels, which carry the blood 
from one part of the body to another, and many small 
cords called Nerves, which pass like telegraph-wires all 
through the body, so that every part seems to know r 
what is going on in other parts. 



QUESTIONS. 
What kind of bodies do we see around us ? 
What do we learn from the study of Physiology ? 
What does the word Physiology mean ? 
How do animals and vegetables differ from one another ? 
What do we learn from Anatomy ? 
Into how many parts do we divide the body ? 
W T hat is the covering of the body called? What are its uses? 
What is the skull ? ♦ 

How is the face made up ? 

What is the skeleton ? How many bones has it ? 
W T hat are the muscles? 

What organs are in the chest ? In the abdomen ? 
What are the uses of the blood-vessels and nerves ? 



THE BONES AND JOINTS. 



The shape of the body depends upon the bones, which 
we have already seen, serve to protect the other import- 
ant organs from injury. As already stated, the brain is 
protected by the skull, and the heart and lungs by the 
walls of the chest. In the interior of the bones of the 
spinal column (Fig. 5) is a delicate part of the nervous 
system, called the spinal cord, which has much to do with 
the sense of feeling and motion of the body and of the 
lower extremities. 

The bones are very different in size : those of the arms 
and legs are large, those of the hands small. This is why 
the hand is so movable and useful for so many purposes, 
as handling objects, writing, etc. could not be performed 
unless there were a number of small joints and muscles 
to bend the fingers in almost every possible position. 

When w r e look at a bone, such as we see it sometimes 
as it comes with the meat from the butcher, it seems to 
be a hard, smooth, or solid body. One would hardly 
think that there was so much that was fluid or delicate 
inside the bone. If this were not so the bones would 
be too solid and heavy. Almost all the bones of the 
body are hard outside, and like a honeycomb inside, 
resembling a sponge. Inside this is a substance called 
the marrow. To see this we have to saw through the 
bone lengthwise, and we at once understand why the 

18 



THE BONES AND JOINTS. 



19 



bones are so strong and at the same time so light, the 
outside of the bone being solid and the inside so delicate. 

Bones are made up of two kinds of matter : one that 
is like jelly, and called animal 
matter; the other hard and 
aarthy. Little children have 
more of the animal matter in 
their bones, while the bones of 
older persons have much more 
of the earthy matter. This is 
why the bones of old persons 
are so easily broken, and why 
the bones of the youngest little 
folks will sometimes bend be- 
fore they will break. When 
the animal part and the earthy 
part are in the proper quantity 
the bones are strong and will 
not easily bend or break. The 
earthy part makes the bones 

hard and firm, while the jelly-like part makes them 
tough and elastic. If we wish to see the earthy part of 
a bone, we drive off the animal part by heat, and what 
is left is like chalk and very brittle. If we wish to see 
the animal part, we place a bone in a weak acid for a 
few hours, and the earthy part is dissolved, leaving the 
animal part in the shape of the bone, but so soft and 
elastic that a knot can be tied in it. 

Bones of the Trunk. — The bones of the trunk or body 
are made up of those of the spinal column or back-bone, 




Fig. 3. — Interior of a Bone. 



20 



ELEMENTARY PHYSIOLOGY. 



those of the chest, and those of the pelvis or hip (Fig. 4). 
The spinal column (Fig. 5) is a series of twenty-six 
bones in a long chain, the bones being smaller at the top 
of the row and larger at the lower part. The spine is a 

strong base of sup- 
port to the chest and 
abdomen. There is 
an opening in the 
centre of each bone 
of the spine, so that 
when all the bones 
come together a ca- 
nal is formed, in 
which the spinal 
cord is placed. This, 
we shall hereafter 
see, is one of the 
great nerve - cen- 
tres, which has much 
to do to direct the 
movements and feel- 
ings of the body. 
Each of these spinal 
bones is sometimes 




Vertebrae of the 
loins. 



Pelvis, 



called 



a ver 



'tebra. 



Fig. 4. — Skull and Bones of the Trunk. 



from a Latin word 
meaning " to turn," 
and the w T hole spinal column is therefore called the ver- 
tebral column. 

The bones of the spinal column do not rub against 



THE BONES AND JOINTS. 



21 



fl 



Vertebrae of 
the back. 



each other or touch one another. Between all these 
bones is an elastic matter, which has the effect of mak- 
ing the whole spine slightly Spines, 
movable. If these bones processes. , 

teUiU1 "i^ )■ Vertebrae of 

were all placed together, 
without this elastic matter 
between them, any fall or 
blow on the spine would 
certainly injure the spinal 
cord, or even hurt the 
brain itself. The effect of 
this may be shown by tak- 
ing several ivory balls and 
hanging them by strings 
alongside of one another. 
Raise up the last one, and 
let it fall against its neigh- 
bor, w T hen the force of the 
blow will be felt through 
all the balls, and the first 
one in the row will fly off. 
If, however, one, or per- 
haps two, soft balls be 
placed in the row, and the 
last ivory ball be again 
brought against it as be- 
fore, the force of the blow 
will be so broken that the 
first ball will not move. The elastic matter between the 
bones of the spine yields so much during the day that 



Vertebrae of 
the loins. 



Fig. 5. — Spinal Column. 



22 ELEMENTARY PHYSIOLOGY. 

we are shorter at night than in the morning after a night's 
rest has taken part of the pressure off the elastic matter. 

The bones of the chest (Fig. 4) are arranged like a cage, 
which is made up by the spine at the back, the breast- 
bone in front, and the ribs passing between them. There 
are twenty-four ribs, twelve on each side. They are 
long and curved, and some of them are fixed to the 
breast-bone, while others are joined to the other ribs by 
elastic matter, which allows them to move easily, so that 
the lower part of the chest yields in the act of breathing. 

The bones of the pelvis (Fig. 4) are very heavy and 
shaped like a basin. They act as a support to the parts 
above, and bear the weight of the whole of the upper 
part of the body. 

Bones of the Lower Extremities (Fig. 2).— These are 
united to the trunk or body where the thigh-bone fits into 
the hip-bone. This is what is called the hip-joint. The 
thigh-bone is connected with two bones of the leg at the 
knee-joint, and where these come together is another 
small bone, called the knee-cap, which fits into the hol- 
low space between these bones. At the ankle the two 
bones of the leg unite with seven small bones, and 
these bones unite with five other bones to form what is 
called the arch or instep of the foot. Next to these 
come a number of small bones, called the phalanges, 
which make up the toes (Fig. 2). 

Bones of the Upper Extremities. — One of these bones 
is the collar-bone (Fig. 4), which is connected with the 
breast-bone in front and the shoulder-blade behind. 
With the latter it gives shape to the shoulder. In the 



THE BONES AND JOINTS. 23 

shoulder-blade is a hollow space or cavity, in which the 
arm-bone moves. This is what is generally called the 
shoulder-joint. There is one bone from the shoulder 
to the elbow, at which point the two bones of the fore- 
arm are connected with it. The two bones of the fore- 
arm are placed side by side, and when the hand is turned, 
as in writing, grasping, etc., one of these bones twists 
around over the other. Where these bones meet the 
bones of the hand the joint is called the wrist. The 
wrist is made up of eight small bones, which look like 
small stones or pebbles, and give it motion in various 
directions. The palm of the hand is made up of five 
small bones, and the fingers and thumb are composed of 
fourteen smaller bones called phalanges (Fig. 2). 

All the bones have a covering to protect them, through 
which blood-vessels pass to nourish or feed them. 

Other animals have their bones differently arranged 
from those of man. When they move about from place 
to place they hold themselves in a very different position 
from that which a man, or even a child, takes for the 
same purpose. If we look at the monkeys in the menag- 
erie, we will see that they do not hold their heads erect, 
and that they are generally stooping and crawling (Fig. 6). 
Man is the only animal that stands straight with his head 
erect. The limbs of animals are arranged so as to be 
adapted to their movements, and they differ from those 
of man also in the number of bones composing them. 

The Joints. — Owing to the large number of bones in 
the human body, especially in the limbs and in the trunk, 
it is very movable ; but this motion would not be possi- 



24 ELEMENTARY PHYSIOLOGY. 

ble to any very great extent if many of the bones were 
not joined together in some way. Suppose, for instance, 
that there was only one bone extending all the way from 
the hip to the ankle or from the ankle to the end of the 



Fig. 6. — Skeletons of Man and Chimpanzee. 

toes, what little motion there would be ! Bending the 
leg could not take place, and walking would be a labor. 
But by having a number of bones placed together or very 
near each other a certain amount of motion can occur ; and 
this is what is meant by a Joint, for a joint is formed by 



THE BONES AND JOINTS. 25 

two bones with short white bands passing between them 
to hold them together. These bands or cords are called 
lig'aments, but a ligament only means something that 
binds one thing to another. 

These cords are very strong, and are in shape like 
pieces of ribbon of different widths, and they yield a 
little when the joints are moved. They are strong 
enough to prevent the joints from being torn apart; and 
in some parts of the body, as the elbow and the knee, 
there is quite a number of these ligaments of different 
sizes, placed all around the ends of the bones where they 
come together to form a joint. The bones would soon 
wear away if the ends of them kept rubbing against one 
another during so many years of life, and so Nature has 
given them a thick elastic covering called cart'ilage, which 
many persons call gristle ; and this comes between the bones 
and protects them from rubbing against one another, with- 
out in any way interfering with the motion of the joint. 
One would think that so much rubbing as must take 
place when the large bones of the leg or of the arm 
are constantly brought against each other in walking or 
writing or bending the elbow, would wear out the carti- 
lages. But this hardly ever occurs, and most persons do 
not know from the wear on them that they have any such 
things as cartilages at all. Perhaps the cartilages would 
often wear out if the joints were not covered by a very 
thin, slippery fluid like white of egg, which is being 
poured over them all the time ; and this joint-oil, as it 
might be called, keeps the bones with their cartilages in 
proper condition for every movement. This is on the 



26 



ELEMENTARY PHYSIOLOGY. 



same principle that the engineer oils his machinery to 
make its joints move easily and without friction. 

Some joints are much more readily moved than others. 
The hip-joint (Fig. 7) is a very movable joint, but the 







Fig. 7. — Hip-joint. 

1, 2, 3, ligaments. The bone in Fig. 7 is represented as moved from its socket, 
so as to show the cavity. In Fig. 8 the ligaments of the elbow appear as it 
separated, for the same reason. 

shoulder is more so, allowing the arm to be turned in al- 
most all directions ; but this is because the thigh-bone goes 
into a much deeper socket at the hip than the arm-bone 
does at the shoulder. Some of the joints are movable in 
several directions • others in one only. The elbow-joint has 



THE BONES AND JOINTS. 



27 



a movement like a hinge ; the hip-joint and shoulder- 
joint are arranged like a ball and socket. Children will 
know what this means when they play cup-and-ball, 
which is itself a sort of ball 
and socket. 

The knee-joint is like a 
hinge, but the wrist-joint 
acts not only in the nature 
of a hinge, but it admits of 
what is called rotation ; that 
is, the joint turns upon itself. 
One of the two bones of the 
forearm turns around the 
other every time the hand 
is laid on its back or on its 
palm. If these bones were 
not thus movable, the hand 
would always remain in one 
of these positions. 

There are no joints in the 
skull like those of the elbow 
or hip or wrist. In early 
life some of the bones are 
movable, so that the brain 
may have room in which to 
grow ; but after a while the 
bones become firmly fixed, so as to be no longer movable. 
If this were not the case the delicate brain would be 
pressed on, and perhaps death would result. 

The spinal column also has ligaments which hold the 




Fig. 8. — Elbow- joint. 
bones of forearm; 2, ligament; 3, 
bone of arm. (In the dotted lines 
the ligaments are shown cut apart, 
so that the joints may be seen ) 



28 ELEMENTARY PHYSIOLOGY. 

bones in place, but the motion between them is very 
slight. They do turn a little upon one another, and that 
is the reason, as already stated, that the name ver'tebrce is 
given to them, from a Latin word meaning " to turn." 
Two of these bones, just where the head is fitted upon the 
spine, are movable, and this is the reason that we can nod 
and shake our heads as we choose. One of these bones of 
the spine is called the atlas, because in ancient fable a 
man called Atlas was said to have carried the whole 
world on his shoulders; the head being the globe which 
this spinal bone bears upon it. 

There are joints also between the ribs themselves, and 
between the ribs and the spine. 

When the large or small cords, called ligaments, which 
connect the bones are stretched beyond what they can 
bear, what is known as a sprain takes place. This is 
how a sprained ankle results from slipping on a pave- 
ment; the ligaments get stretched too far, and almost 
speak of their own sufferings when they express the 
feeling of pain. Sometimes the ligaments are torn apart, 
if the force of the fall or of the accident should be great, 
and, as they do not heal easily or rapidly, the joint re- 
mains weak for a long time. 

Sometimes bones get out of place, when they are said 
to be " dislocated," or out of joint, but this accident is 
more likely to happen in such a joint as the shoulder, 
because it is so very movable and the socket into which 
the bone fits is not deep, so that the bone slips out very 
easily. 

Young bones are soft at first and have the proper shape. 



THE BOXES AND JOINTS. 29 

but they do not become hard, like bone, until the earthy 
matter is deposited in them, when they become firm and 
rigid. If a bone be broken, it heals very much in the 
same way ; that is, at first a thin fluid substance is poured 
out at the broken parts of the bone, and soon after an 
earthy or mineral matter is deposited, which unites with 
the other to form bone. In a few weeks, if the bones 
have been kept at rest and closely bound together by 
bandages and other means which the ready surgeon has 
at hand, the broken pieces will be again united, and the 
bone at that point may be stronger than ever. 

Hygiene of the Bones. — We must do all we can to 
keep ourselves free from sickness, and children can often 
do this themselves if they understand what are the best 
rules for keeping well. So far as their bones are con- 
cerned, they must remember that when they are very 
young these are very much more easy to bend than when 
the child grows to be a man or a woman. They must be 
particular, therefore, as to their position in school, at 
home, or wherever they may be. When a baby first 
begins to walk, if its legs are not strong enough to bear 
its weight they will become bowed, and what is known 
as " bow-legs " may result. Children should be very 
careful as to the position they take in sitting at their 
desks ; they should not get into the habit of leaning 
over too much or of twisting their bodies, or of sitting 
in ungraceful attitudes, as they will soon get their backs 
twisted or their shoulders rounded. 

The bones of children sometimes become weak and 
badly deformed, and almost like wax in softness, from 



30 ELEMENTARY PHYSIOLOGY. 

the fact that they have not been fed upon the kind of food 
to give them plenty of mineral or earthy matter for their 
bones. Sometimes they may take too much of this kind 
of matter, and the bones will then become like those of 
an old person, having too much earthy matter and being 
very likely to break from the slightest injury. Exercise 
and fresh air and a good diet will do more than anything 
else to preserve the good health of the bones. 

Effect of Alcohol on the Bones. — Children should 
know, from the first moment that they learn physiology 
or hygiene, that every organ of the body may be injured 
by the use of alcohol or liquor in any form. Sometimes 
only one organ is affected at first, but gradually all the 
rest follow, and sooner or later very bad health results, 
or even death. It is commonly believed that the healthy 
growth of any part of the body may be checked by the 
use of alcohol or tobacco, and the bones may therefore 
be stunted in their growth or affected in their health by 
the use of these articles. The children of drunken 
parents may thus inherit a tendency to disease of the 
bones which may seriously affect those organs in child- 
hood, or even in after life. 



QUESTIONS. 

How are the eye and the ear and the heart protected from injury? 

How is the inside of a bone arranged ? 

What two kinds of matter is bone made up of? 

What effect has each kind on the bone ? 

What are the bones of the trunk ? 

How is the spinal column made up ? 



THE BONES AND JOINTS. 31 

"What is the use of the elastic matter between the bones of the 
spine? 

How can you show this? 

Which are the bones of the chest? Describe how the ribs are 
arranged. 

What is the pelvis? 

What are the bones of the lower extremity? 

How are the thigh-joint and knee-joint formed? The ankle-joint? 

Describe the bones of the arm and forearm. 

How many bones in the hand? 

How are the bones covered ? 

How are the bones in man different from those of other animals? 

What are joints intended for ? 

What are the ligaments for? 

How are the bones covered at the joints ? 

What is the use of the fluid in the joints ? 

What are the different kinds of joints ? The hip ? The elbow 9 

Are the bones of the skull movable ? 

Is there anything peculiar in the bones of the spine ? 

What is a sprain? What is a dislocation? 

How do broken bones get well ? 

Does the kind of food have any effect on the bonef ? 

Has alcohol any effect on the bones? 



THE MUSCLES. 



When we move the body or any part of it, we do so 
by means of fleshy matter connected with the bones to 
which the name Muscles has been given. These give 
shape and fulness to the different parts of the body. 
There are more than four hundred muscles in the human 
body. The red meat or flesh we are familiar with in 
the butcher's shop is muscle. Every action which an 
animal goes through is produced by the action of a mus- 
cle or a set of muscles. When we speak or wink or move 
a finger to write or to grasp anything we move muscles, 
as we also do when we laugh or sing. When a dog 
barks or a horse runs or a bird flies, it has to use a 
muscle or muscles. We find muscles in every part of 
the body : some of them are small and hardly to be seen 
without a magnifying glass ; others, like those of the 
arm or leg, are large and thick. 

Many of the muscles are found near the joints, 
placed in such a way as to move the limbs ; some of them 
are deeply seated in the inner parts of the body. Where- 
ever we find a muscle, no matter how small, it means 
motion in some shape or other. 

When muscles are examined under a microscope they 
are found to be made up of a large number of fibres or 
fi'brils, as they are called, placed alongside each other in 



32 



THE MUSCLES. 



33 



regular parallel lines (Fig. 9). These are so small that 
they cannot be seen with the naked eye, but they are the 
portions of the muscle that contract and cause action in 
the part to which they are fixed. These fibrils are ar- 
ranged in bundles, and each muscle has a number of these 
bundles ; the fibrils being 
made up of little round bod- 
ies or discs, like coin, placed 
on top of one another (Fig. 
9, a). Every part of these 
fibrils has the power to 
shrink upon itself and short- 
en itself; and when all act 
together the whole muscle 
contracts or shortens itself, 
and the two ends of the 
muscle are brought nearer 
one another. 

One of the best modes 
of studying this action of a 
muscle is to grasp the left 
arm between the elbow and 
the shoulder, and, while 
holding it in this position, draw up the left hand so as 
nearly to touch that shoulder, when a round fleshy mass 
will be felt under the right hand. This is caused by the 
muscle or muscles of the arm contracting or shortening, 
and at the same time drawing up the forearm with 
them. 

As some of the muscles are placed upon the arm or 

3 




Fig. 9. — Fibrils of Muscle. 
A, B, muscular fibrils ; A', cross-section 
of one of the discs composing them, 
the fibril being stretched open to 
show the arrangement of the discs. 



34 ELEMENTARY PHYSIOLOGY. 

the leg in such a way as to bend the limb upon itself at 
the elbow or the knee, so other muscles are placed upon 
the same limbs in such a way as bring the arm or the leg 
back again to the same position it was in before it was 
bent. 




Figs. 10, 11. — Actions of a Muscle illustrated (the other portions of the 
arm having been removed to show the action of the muscles more dis- 
tinctly). 

We can move many of the muscles at our own will, 
but there are many of them, too, that will go on con- 
tracting during our whole lives, and we cannot stop them 
from contracting. The heart is made up entirely of 



THE MUSCLES. 35 

muscles, but it will go 011 beating as long as we live, 
without any power on our part to check it ; for the beat- 
ing of the heart is nothing: more than a series of contrac- 
tions of these muscles. When we breathe we move the 
muscles of the chest up and down, and we also call into 
use some of the muscles of the abdomen. When we 
sleep we are still using the same muscles for breathing 
with ; and this is the best proof that muscles can go on 
contracting when we are not having any will-power in 
the matter. The blood goes on flowing through the body, 
and what we have eaten is digested and passes on along 
the stomach and bowels, all through the action of mus- 
cles, whether we are asleep or awake. 

All muscles must take a rest after they have been do- 
ing their work. After they contract they gradually go 
back to their former place, and rest until they are called 
upon to do their duty again. Even the heart after each 
beat takes a rest or pause for a short moment, until it is 
ready to give another beat. If we bend the arm or keep 
it stretched out in a straight line, it will soon feel very 
tired ; and this is because the muscles that bend it or 
keep it on the stretch want rest. 

The bundles of muscular fibres are covered by a 
thicker membrane, which forms, at the end of the mus- 
cle, where it is connected with the bone, a tough sub- 
stance called a tendon (Fig. 12). The muscles are soft 
and delicate, and w r ould tear away from the bone if the 
force were exerted upon them alone. The tendon is 
white and smooth and shiny, and when the muscle con- 
tracts the whole force is exerted through it. We can 



36 



ELEMENTARY PHYSIOLGY. 



feel a tendon just beneath the skin at the back part of 
the knee, and a very large one — the largest in the body — 
behind the ankle. Through this last one the large mus- 
cles on the back of the leg act upon the foot, as in walk- 
ing and other movements of the leg. In ancient fable 
this was said to be the only part of 
the body of Achilles, a great Gre- 
cian warrior, which was not proof 
against injury from any weapon of 
war, and so this tendon has always 
been called the tendon of Achilles. 
The tendons and the white shin- 
ing membrane which cover the 
muscles of the arm and the leg 
give shape to those limbs and di- 
minish their size (Fig. 13). If 
they were not so covered the mass 
of muscles would have an ungrace- 
ful effect in their action, and the 
limbs would be clumsy and awk- 
ward. 

Some of the most interesting ten- 
dons are those which move the fingers. The muscles are 
attached to the two bones of the forearm, and the ten- 
dons of these muscles pass down over the wrist and the 
palm of the hand, and are fastened to the bones of the 
fingers. When we bend the fingers we do so through 
those muscles, which pull upon the tendons connected 
with the fingers. There are muscles on the back of the 
forearm which, through other tendons, open the hand in 




Fig. 12. — Tendon of 
Achilles at the back 
part of the leg. 



THE MUSCLES. 



37 



the same general way that the hand is closed by those 
just mentioned. By placing one hand over the wrist of 
the other hand, and closing the latter, we will feel some 
of these tendons in action. 

Movements. — When we 
walk or run or leap or swim, 
we call the muscles into play 
in different ways. 

In walking we use the mus- 
cles of the leg to bend the leg 
or the knee and to bring it 
back again to a straight posi- 
tion, and we also use the mus- 
cles of the thigh, for w T alking 
is a series of movements by 
which we first push forward 
one limb and then the other, 
and at the same time the body 
moves forward. 

When we run, we raise one 
foot from the ground before 
the other reaches it, and w r e 
push the body forward at each 
step. All this is done by the 
muscles of the leg and thigh. 

Some Interesting Muscles. 
— We have mentioned sev- 
eral of the large muscular masses of the body, such as 
those of the leg and arm ; but there are many others 
that are peculiar and interesting on account of their 




Fig. 13. — Muscles of the Leg ; 
covered with membrane. 



38 ELEMENTARY PHYSIOLOGY. 

shape or size or the mode in which they are inserted. 
There is a muscle, for instance, which gives roundness to 
the mouth and causes it to assuni3 the O-shape seen in 
yawning. There are tiny muscles which move little 
bones in the inside of the ear, as we shall hereafter 
learn when we study the subject of Hearing. There 
are strong muscles that help us to chew our food, and 
when we puif out our cheeks we do so by the aid of a 
muscle which is sometimes called the trumpeter's muscle. 
There are muscles connected with the air-tubes through 
which we breathe which are so small that we must use a 
microscrope to see them. Some of the muscles are shaped 
like fans, some are round, others are flat. When we move 
our eyes we do so by means of half a dozen muscles which 
turn the eyeball one side or another or raise or lower it 
at our will. 

Hygiene of the Muscles. — As it is the duty of mus- 
cles to be moved, they must not be allowed to remain 
idle. Muscles that are not called upon to do work be- 
come weak and unhealthy, and the large ones flabby, 
especially in young and growing persons whose muscles 
are not fully developed. Proper exercise is necessary to 
give the muscles full strength and health, and to cause 
the blood to flow actively through them. When the 
muscles are properly exercised, all other parts of the 
body become fully developed also. The brain then be- 
comes more active, and the blood flows rapidly through 
the other organs, such as the liver and stomach. The 
proper exercise of the muscles also gives better shape to 
the limbs, but exercise must not be carried beyond the 



THE MUSCLES. 39 

strength. Exercise should be taken regularly and in the 
open air as much as possible, as breathing the pure air is 
of great importance. 

Exercise should not be taken immediately after a full 
meal, as the stomach is then busy with its own work, and 
the food will not be properly digested if the blood that is 
required there be called away to assist in the work that 
the muscles have to do. Active exercise should jiot 
be taken before breakfast, when the body needs food, or 
in the evening, when it is tired out. 

Children, and young persons generally, should not 
carry their play or exercise beyond their strength. 
They should stop before they become fairly tired out, 
for they become unfitted for any other work or for study 
when so much exhausted. Jumping rope, for instance, 
or racing, may sometimes bring on bleeding at the lungs 
or heart disease or headaches, and children often make a 
great mistake in taxing their strength to see which of 
them can run the fastest or the farthest, or, in jumping 
rope, which can count the largest number of times. 

Muscles grow in size and become stronger according to 
the use to which they are put. A brawny blacksmith's 
right arm is larger than his left, because he uses the mus- 
cles of that side regularly and actively. If he were to 
give up work for a w^hile, his arm would soon grow 
smaller, for the muscles w r ould not be called upon for 
their usual exercise. 

We have spoken of the muscles as being the cause 
of motion in every part of the body. When we smile 
or cry, or become angry or look sorry or grieved, it is 



40 ELEMENTARY PHYSIOLOGY. 

because we use some of the muscles of the face to express 
our feelings of joy or sadness. The face is all made up 
of muscles fastened to the bony framework beneath it. 
It would be well for the young reader to compare the 




Fig. 14. — Muscles of the Face and Neck. 

appearance of the bare skull seen in Fig. 1 or Fig. 5 with 
the same when it is covered with muscles, as in Fig. 14. 
It is through all these muscles, with the smaller ones be- 
neath them, that every movement of the face is made 
and all our pleasant and unpleasant expressions are 



THE MUSCLES. 41 

effected. The muscles of the eyelids, nose, eyebrows, 
lips, cheeks, and tongue all aid in giving expression to 
the face. There are about seventy pairs of muscles con- 
nected with the face and neck. 

Action of Alcohol and Tobacco on the Muscles. — Alco- 
holic liquors affect the muscles in various ways. Of course 
the muscles cannot act properly unless the nerves going to 
them are in a healthy condition. The staggering of the 
drunkard shows that his muscles are not under proper 
control, and that the nerves governing the muscles are 
weakened or perhaps over-excited. As the brain is also 
affected, he cannot give his attention to such steady or 
delicate movement of his muscles as would be necessary 
for fine work. In this way the best workman, although 
he knows exactly what to do when sober, soon loses his 
power to do good w r ork, and clumsily tries and fails. In 
time the voice becomes thick, because he cannot control 
the muscles of his throat or tongue, and he "sees double/' 
because he cannot move the muscles of his eyes properly 
together, his mind also being obscured. 

In training a person for a race or for active exercise 
for a prize, he is not allowed either alcohol or tobacco, 
because they are known to weaken muscular power by 
acting injuriously upon the nerves supplied to the mus- 
cles. It is well for the young to learn as early as possi 
ble that tobacco will have this effect on the nerves sooner 
or later, and will weaken the muscular system, and also 
the other organs, as the heart and stomach. They should 
understand that it is wrong for them to do anything that 
will prevent their muscles or other organs from getting 



42 ELEMENTARY PHYSIOLOGY. 

their full strength and health during their years of child- 
hood or youth. The use of alcohol or tobacco in any 
shape will certainly stunt their growth and development, 
and make their after-life miserable and unhappy ; but we 
shall learn more about this hereafter, when w r e come to 
study the physiology of those organs. 



QUESTIONS. 

What are muscles, and how many of them are there in the body? 
What is the use of the muscles ? 
What are muscles made of? 

How is the action of the muscles of the arm shown ? 
Show how the muscles act in breathing or in the beating of the 
heart. 

Why do the muscles need rest ? 

What are tendons? and what are their uses? 

What kinds of movements occur in walking and running ? 

Describe some interesting muscles. 

What effect has exercise upon the muscles? 

What are the best times and rules for exercise? 

What effect have muscles upon the face? 

How does alcohol affect the muscles ? 

How does tobacco affect them ? 

Why should young persons avoid the use of alcohol and tobacco ? 



DIGESTION. 



The body is constantly wearing out, and we have to 
take food to build it up again. As we have said before, 
the body has been compared to a piece of machinery. 
If the steam-engine or machine is not regularly supplied 
with water and with fuel, such as coal or wood, its action 
will soon stop. So it is with the human body, which 
without the proper amount of food and drink would 
soon fail to carry on the work which its various organs 
have to perform. The muscles and bones, the heart, 
lungs, and skin, are all built up and nourished by the 
food taken into the stomach. The food we eat becomes 
a part of ourselves and keeps us alive. Some waste 
is going on all the time. Every time we move a 
muscle we lose some small portion of ourselves, which 
must be built up again by the food that we take 
into our mouths. The kind of food we eat must be 
something that when taken into our bodies will be like 
the body itself, and must be eaten in such a quantity as 
to take the place of all that we have lost by the wear of 
the organs. If the food is not of the right kind, or if it 
be too small in quantity, the body will soon weigh less 
than it did before. 

The process by which the food which we take into the 
mouth is changed so as to build up our systems is called 

43 



44 ELEMENTARY PHYSIOLOGY. 

Digestion. The food is changed in the mouth and in the 
stomach and bowels, and as it passes along everything is 
taken from it that will be likely to be of use in building 
up the body. 

The Food of Man. — As a rule, the food of man is ob- 
tained from animals and vegetables, but some mineral 
articles are also used for the same purpose. Water, for 
instance, is one of the necessary articles of our daily food. 
It is not only drunk as water, but it is part of many 
of the fruits that we eat. In some parts of the world 
grain and fruits of all kinds are very abundant, and 
many of the people of those countries live on that kind 
of food. In other countries, where there is not much 
vegetable life, the people live almost entirely on animal 
food. 

As we have already said, the body is always wasting 
or losing, and food is necessary to make up this loss. 
While young children are growing the body gains by 
the taking of food much more than it loses ; but after a 
while, as we grow up to be men, the body does not gain 
more than it loses, and the weight remains about the 
same for many months or years. Then, as we get to be 
very old, perhaps we may lose more by the wear of the 
different organs than we gain by the food we take, and 
so we lose in weight. 

The kind of food which we ought to take should be 
such as our systems need. It should be as simple as 
possible for young children, whose stomachs will not 
bear as much in quantity or variety as those of older 
persons. The articles of food should be as much as pos- 



DIGESTION. 45 

sible those which do not require much action in the 
stomach to change them into the kind of material which 
the body needs for its support. This is why milk is the 
best article for very young children to take, for it is full 
of nutritious matters, and, being very much like the 
blood in its composition, does not require the stomach to 
do much work in order to make it ready to pass into the 
blood, and thus go to every part of the body to feed the 
various organs. 

AVe shall see, after a while, that all these matters which 
feed and nourish the body do so through the blood as it 
flows to every part. The milk is like the blood, because it 
contains fatty matter and sugar and mineral and animal 
matters, just as the blood does. Flour is also like the 
bl6od in having the same kind of materials in it ; and 
this is why bread is correctly spoken of so often as the 
" staff of life/' for we can take nothing, except perhaps 
milk, which can be better fitted for our wants, and that 
needs so little change in the stomach to make it like the 
blood. 

There are some articles that are found in almost every 
part of the body, such as salts of iron and lime, common 
table-salt, etc. Some of these are in the teeth and bones, 
and others are in almost all the other organs. When we 
examine the blood and the sweat we find them there, and 
as the body needs salts so much w r e must take them with 
our food ; and this we do in many of the articles we eat, 
without knowing that they are present in them. Even 
the water we drink has many of them in it. Common 
table-salt is taken in small quantity by almost everybody, 



46 ELEMENTARY PHYSIOLOGY. 

usually to give flavor to the food ; but the body needs it, 
and some writers think it helps to make the digestion of 
the food go on more actively in the stomach. It should 
not be taken in large quantities, however, for this mode 
of using it creates thirst- and leads to the taking of 
such an amount of water as to disturb the action of 
the stomach or to dilute the other articles of food more 
than is proper. 

Among the other mineral matters in the body is 
iron, which is found in the blood and other parts. It 
is said that there are about forty-five grains of iron in 
the whole body. This does not seem a very large quan- 
tity when we think that a man of full size usually weighs 
about one hundred and fifty pounds ; but part of the iron 
is found in the coloring matter of the blood, and when 
we consider that a drop or two of some chemical substance 
placed in a tumbler of water will change in a moment the 
color of the whole quantity of water, we can apply this 
fact to the presence of iron in the blood, and understand 
a part of the work the iron has to do in regard to the 
coloring matter of that fluid. Unless there is a certain 
amount of iron in the body, the child or man gets pale and 
unhealthy-looking, and has sometimes to take some form 
of iron as a medicine to bring back his healthy color. 

Gums, Starches, and Sugars. — A great variety of 
articles of food is taken by the people of all nations, 
in addition to the usual meats and vegetables which 
are found in almost all countries. We take starch 
in some form or other when we eat potatoes, rice, 
barley, corn, beans, chestnuts, almonds, or arrow-root. 



DIGESTION. 47 

We find about a pound of starch in every seven pounds 
of potatoes. We take sugar in some form whenever we 
eat carrots or melons or turnips, and especially when we 
eat honey or fruits. It seems singular to find sugar 
in the human body in such organs as the muscles — those 
of the heart, for example. There is a kind of starch 
in the liver which is afterward changed into sugar. We 
take fat into our bodies whenever we eat butter or lard 
or sweet oil. Gummy matters are sometimes used for 
food. They generally flow from trees by making cuts 
into them at the proper season of the year. Gum-arabic 
is collected in this way. Gums are not good as articles 
of food, for they are not easily digested in the stomach. 

Albuminous Substances. — In many of the most useful 
articles we eat there is a substance called albu'men, which 
is so called from the Latin word albus, meaning "white," 
because it is like the white of an egg. If we do not find 
the albumen itself, we find other articles resembling al- 
bumen, which are therefore called albu'minoid, or "like 
albumen." These are the kinds of food that seem to be 
best adapted for the building up of the body, and also 
for keeping it warm. White of egg itself contains a 
large quantity of albumen. The articles that are like 
albumen are called fi'brin and ca'sein. Lean meat and 
wheat bread contain both fibrin and casein. The curdy 
part of milk is casein, for the word casein really means 
" cheesy." What is called " curds and whey " is only 
the casein of the milk made into a curd. Fibrin is found 
in the blood and in the muscles. 

Fats. — Fat is found in the body under the skin and 



48 ELEMENTARY PHYSIOLOGY. 

in many of the organs, even in the blood. Fatty mat- 
ters keep the body warm, and also help to nourish it. 
We therefore take fat or oil in our food when we eat 
meats or oily grains or seeds, butter, etc. Fats are eaten 
largely by those who live in very cold regions, such as 
those in Arctic countries, and they help to keep up the 
warmth of the body. Even tallow candles and the 
coarsest oils are used for this purpose. 

A mixture of different kinds of food should be taken 
at each meal, for the simple reason that any one article 
of diet may not be enough to supply the exact kind that 
the body may at the time require to build it up. It is 
better, however, to eat plain food, such as lean meat, 
eggs, milk, or bread, with nourishing vegetables and per- 
fectly ripe fruits, rather than take fatty or rich articles 
that give the stomach too much to do or overload it with 
perfectly useless matters. 

Nitrogen. — The air that we breathe is made up of sev- 
eral gaseous matters, the two most important of which 
are called ni'trogen and ox'ygen. The food which we 
take into our stomachs contains a certain quantity of both 
these substances. We need not for the moment consider 
oxygen as a part of the food, but may briefly say that 
some writers divide all articles of food into two kinds — 
those which have nitrogen in them, and those which have 
not. Vegetables, as a rule, have little or no nitrogen in 
them ; animals have it in large quantity ; so when we 
eat meat we take into our stomachs a certain amount of 
nitrogen, which the body actually needs for its healthy 
work. It is better to eat a mixed diet of both animal 



DIGESTION. 49 

and vegetable food, however, as the body, with its great 
variety of organs, needs just such articles as are thus to 
be obtained, for if they do not contain any nitrogen, they 
may have other substances in them which will help to 
meet the wants of the body. 

As vegetables contain but little nitrogen, and some of 
them do not contain any, we would have to eat a much 
larger quantity of them to get from them the amount of 
nitrogen that we actually need than if w r e eat animal food. 
It is said that a horse must eat three times as much veg- 
etable food, in proportion to its size, as a dog does of 
animal food, to get the same amount of good from it. 

Variety Necessary. — Variety of food is necessary to all 
animals that are in the habit of taking mixed food. If 
a dog, for instance, which has been in the habit of eating 
everything that it could get hold of, were locked up or 
kept by itself in a place in which it could only eat one 
kind of food, it would soon begin to droop away and 
perhaps die. A man who has been in the habit of eat- 
ing meats and vegetables will soon get sick if he is fed 
for any length of time on meat alone or vegetables alone. 
This is the reason that the Government when it arranges 
what its soldiers and sailors shall eat gives them a vari- 
ety of different kinds of food, so that they shall keep 
healthy and strong, and not get a disease called scurvy, 
which will be very apt to attack them if they eat too 
much of one kind of food. 

We have stated that albuminous articles are the best 
for the stomach and for the body itself. Meat and milk 
have albumen in large quantities in some form or other. 

4 



50 ELEMENTARY PHYSIOLOGY. 

The egg contains, besides the yolk, scarcely anything but 
albumen, and from it the whole chicken — its feathers, 
claws, blood-vessels, and everything that goes to make 
up the animal — is formed. This is a good point to show 
how very important albumen is to the life and growth 
and health of this animal and of every other animal, for 
all animals need just such life-giving and health-support- 
ing materials. 

Animal Food. — Almost all parts of animals have been 
used as food, but the portion usually eaten is the flesh, 
wdiich, we have already stated, is the muscular part. The 
meat of very young animals should not be eaten, because 
it is not easily digested, and the fat is not mixed with 
the fibres of the meat as it is when the animal is older. 
When fat is well mixed with lean meat, as in the ox, the 
meat is more digestible. In the very young calf, the veal, 
as it is called, has fat around it instead of being mixed 
through it, and it is more jelly-like, and therefore not so 
easily digested. 

Almost all parts of birds have been eaten as food, but 
any part of the animal which is always in use is not so 
tender. Chickens' legs are not so good for food as the 
wings. A duck's leg is not used so much, and it is there- 
fore quite as good for eating purposes as its wings. Birds 
that live in the water, such as the goose or the duck, do 
not have as tender meat for eating purposes as those which 
live on the solid ground, such as chickens ; the fat mixed 
with their flesh is more fishy. 

The flesh of fish is much used as an article of food ; it 
is made up mainly of albuminous materials, but is not 



DIGESTION. 51 

so nourishing as the meats usually eaten, although more 
so than a purely vegetable diet. ' Oily fishes, as the eel, 
are not easily digested in the stomach. Tribes are found 
in various parts of the world who live on fish alone, that 
being the food which they can easily secure, after floods 
or heavy rains, with little trouble and expense. Nearly 
every part of the fish is considered good for food. A fish 
diet has been recommended to those who are tired out 
with heavy brain-work, because it contains a chemical 
substance called phosphorus, and as this stimulating sub- 
stance is always present in large quantity in the brain, it 
lias been thought that this organ would receive a fresh 
supply when this kind of food is taken. 

Milk. — As already stated, milk is well adapted to sus- 
tain life, being composed of such albuminous matters, fats, 
and sugars, in water, as will nourish the body. When 
taken into the stomach it is changed by the fluids of that 
organ into a solid curd and a fluid or whey. The curd is 
digested just as any other substance would be digested 
there, while the fluid portion is taken into the blood- 
vessels, and soon becomes a part of the blood itself, 
going to the nourishment of all the living organs. The 
cheesy part of the milk sometimes disagrees, from its not 
being digestible, and the curd formed in the stomach may 
remain there for hours. Generally, milk agrees bettei 
than any other kind of food. Boiling makes milk much 
more digestible, especially if a little lime-water be added 
to it, if there is an acid state of the stomach. 

From milk we get cream, butter, cheese, buttermilk, 
and whey. Cream, carefully skimmed from the milk, 



52 ELEMENTARY PHYSIOLOGY. 

contains casein and whey, together with the butter. It 
is not as digestible as milk, because it has more fat or oil 
in it. For this reason butter, which is the oily part of 
milk, obtained by churning, is, like other oils, not very 
digestible. Cheese, which is the curd of milk pressed 
and partially dried, carrying with it a little butter, is 
very nourishing, but not very digestible. An old prov- 
erb says — 

" Cheese is a surly elf, 
Digesting all things but itself," 

because it is thought that it helps to digest other articles 
of food that may be keeping its company in the stomach. 
Cottage-cheese or smeer-case — the soft curd of milk — is 
more easily digested. Buttermilk is the fluid left in the 
churn after the butter has been taken away. It has lost 
the greater part of its fatty matter by churning, and 
should therefore be more digestible, though not so nour- 
ishing. Whey contains a little sugar, cheese, and butter, 
but is apt to turn acid in the stomach. 

Eggs. — These are more nourishing than milk, but not 
so digestible. The white of the egg is almost wholly 
albumen in a pure state; the yolk is oily matter with 
albumen. When heated, the white of the egg, or albu- 
men, becomes cloudy or thick, and is then said to coagu- 
late. It is more digestible when slightly boiled than 
when raw. The yolk, on account of its fatty matter, is 
not so digestible. One great advantage of the egg as an 
article of food is the large amount of nourishing matter 
contained in a small space. Fried eggs are not very di- 
gestible, for the albumen becomes hardened and the oily 



DIGESTION. 53 

matter is altered by the heat, so as to be unfitted for 
digestion. All substances that contain a large amount 
of food in a small compass are digested by the stomach 
with difficulty. 

Vegetable Food. — In some portions of the world vege- 
table food is almost the only diet, and there are many 
animals that live entirely on this kind of food. As 
already stated, animals contain much nitrogen ; we 
may then ask, How does the flesh of such vegetable- 
eating animal get the nitrogen of which it is composed 
if there is none in its food? The air it breathes 
is largely made up of nitrogen, and this is doubt- 
less the chief source of its supply, passing into the 
animal's lungs, and afterward into every portion of its 
body. 

Bread is usually made from the flour of wheat. It 
contains a sugar or starchy matter and a thick gluey al- 
buminous matter called gluten. When yeast or paste is 
added to it the bread is said to be leavened. The yeast 
or the paste acts as a ferment, as it is called ; that is to 
say, just as soon as it is added it begins to affect the 
flour, until it changes the whole character of the mass 
into which it has been introduced. It is necessary that 
there should be ferments in the human body ; we find 
them always present in the mouth, in the stomach, and 
in the upper part of the bowels; and wherever they 
are, we find that it is their duty to be getting the food 
into motion, stirring it up and changing its composition 
until it is fit to be taken into the blood for the nourish- 
ment of the body. 



54 ELEMENTARY PHYSIOLOGY. 

Sweet cakes and pies are not very digestible, for they 
are generally made up of sugar and eggs. They should 
be eaten sparingly for this reason. 

Breads are made also of other flours, as bran, rye, bar- 
ley, etc., but they are not so digestible or nourishing as 
that prepared from wheat, and are apt to turn acid in 
the stomach. Rice and corn flour are also eaten as bread, 
and are both digestible and nutritious. 

Fruit. — By some persons fruits are considered as the 
most healthful articles that can be taken into the stom- 
ach ; by others they are looked upon as a source of 
stomach trouble. As a rule to be generally observed, 
fruits should be eaten only when perfectly ripe, and 
the seeds and skins should not be swallowed, for they 
are thoroughly indigestible. Such fruits as the melon 
and canteloupe are the least digestible of all this class. 
Preserved fruits may disagree with the stomach, just as 
sugar does, although the mixture of fruit with sugar is 
not so likely to disorder the stomach as either sugar 01 
fruit alone. 

Cooking. — The value of food depends upon its being 
digestible and upon the amount of materials it contains 
with which to nourish the body; but the manner of 
preparing the food in cooking is also important. Few 
articles of food are ready at once to be taken into 
the stomach without being cooked. In this way the fla- 
vor of the meat is brought out or new flavor added, and 
the article itself made digestible by the softening and 
dividing of its particles, either before or during the cook- 
ing, by chopping or cutting or by the aid of heat or 



DIGESTION. 55 

water or salt. By heat especially the most active parts 
are often entirely separated. 

Drinks. — The drink of all drinks to be used by man 
should be water alone. It is needed by the body for va- 
rious useful purposes, being especially required to keep 
the different tissues moist and soft. It will surprise 
many young readers to learn that water is found in some 
of the most solid parts of the body, as the teeth and the 
bones and in the muscles. About two-thirds of the 
weight of the body is water. When we say that a man 
weighs a hundred and fifty pounds, we know that one 
hundred pounds of this is water. Nearly a fourth part 
of his bones is water, and about three-fourths of his skin 
and of his brain and of his muscles. Milk and blood 
are very largely composed of water, and the tears have 
scarcely anything else in them. 

A man can live for a longer time without solid food 
than he can without water, so necessary is it to his life 
and health. For drinking purposes, water should be 
perfectly pure, for if impure it may give rise to severe 
sickness, such as typhoid fever. The amount of drink 
necessary for an individual to take in the twenty-four 
hours depends on habit, for some persons can take a large 
quantity, while others, equally healthy, use but little. 
Whatever the system requires must be taken. If solid 
food is swallowed too rapidly, the fluids in the mouth 
cannot soften it, so that it will be necessary to swallow a 
considerable amount of water to produce that effect. The 
amount of water or other liquid swallowed at meals 
should not be very great, as the food becomes too much 



56 ELEMENTARY PHYSIOLOGY. 

softened, and the fluids of the stomach are so much di- 
luted that they will not act properly on the food. Acid 
and sweet drinks, or drinks of any kind, should be 
avoided immediately before meals, as they excite the 
stomach to action before the food is taken. Hot drinks 
stimulate the stomach to increased secretion, and at the 
same time increase the action of the muscles of that 
organ ; but if we get into the habit of exciting the stom- 
ach in this way, we injure it, and finally weaken it. 

For drinking purposes, rain-water and water from 
springs, rivers, wells, and lakes are used ; but river-wa- 
ter, which is obtainable usually in larger quantities, is 
generally used. It sometimes contains impure matters 
that have been emptied in it from factories or dwellings, 
or decayed animal or vegetable matter carried into it 
from smaller streams. If water is not pure, it should 
be filtered or boiled. Boiling kills the germs of disease 
that may exist in the water. Filtering with charcoal 
takes away the solid impure matters and removes any 
bad odors from the water. Sometimes the impure mat- 
ters may be driven off by distilling the water ; that is, 
the water is heated until it passes off in the form of vapor 
or steam, and then as the vapor cools it will be collected 
again, drop by drop, as water in another vessel. 

Alcoholic Drinks. — Cider, wine, beer, whisky, and 
brandy are forms of alcoholic drinks commonly used. 
Some of them, such as cider and beer, have only a small 
quantity of alcohol in them ; while others, such as whisky, 
brandy, and rum, contain a very large quantity of alco- 
hol. The power which they have of intoxicating is due 



DIGESTION. 57 

to the alcohol. Although the amount in cider and beer 
is quite small, it is better to avoid their use entirely, 
because they may lead to the habit of taking alcoholic 
drinks. Beginning with cider or beer, the drinker will 
not be long in getting into the habit of taking stronger 
liquors, as brandy or whisky. 

Alcohol is a clear, colorless liquid, lighter than wa- 
ter, and is formed as the result of a process called fer- 
mentation. The grape, the melon, and other fruits, and 
rice, have been used for this purpose. These articles 
contain sugar, and when fermentation takes place alcohol 
is formed as one of the results. The gas which bubbles 
up in it is called carbonic acid. Wine is usually made 
by the fermentation of grapes ; cider, by the fermentation 
of apple-juice. 

Alcohol is not a food, for it does not nourish the body 
or help to build it up when it is wearing out. It gives 
rise to thirst, which we shall soon learn is the desire for 
more drink. It takes water from the other parts, where 
the water is needed for better purposes. The alcohol 
passes into the blood, and is not changed as true food 
would be. It does not relieve hunger, which is a desire 
for solid food. It does not help other articles of food to 
be digested. It does not warm the body, as some persons 
might think. It may flush the face, but that is because 
the little nerves which control the small blood-vessels of 
the face are deadened, and the blood fills the vessels and 
keeps them full all the time, so that the face is reddened. 
Besides all this, poisons of various kinds are sometimes 
mixed with the whisky or rum sold in the saloons, and 



58 ELEMENTARY PHYSIOLOGY. 

the alcoholic drink is made still more dangerous to take. 
Aloes, strychnine, jalap, copperas, and other injurious arti- 
cles are used for this purpose. 

Alcohol acts as a poison on the stomach and bowels. 
At first it causes sickness of the stomach, or the food 
taken into the stomach does not agree with the person 
taking such drinks ; and after a while the lining of the 
stomach gets diseased and inflamed, and the person dies. 
The worst effect of these alcoholic drinks is upon the 
liver, for as soon as they are swallowed they pass into 
the stomach and go at once to that organ. Soon the 
liver becomes yellow and looks like a lot of hob-nails, 
and the drinker dies after much suffering and sickness. 

Alcohol should be looked on as a medicine, and only 
to be taken as such, and not as either food or drink. It 
is really a poison, and the sooner we regard it as such the 
better it will be for the health and happiness of us all. 
As a drink it should be avoided as if it were an enemy 
to human life. It is the cause of hundreds and thousands 
of cases of sickness, and some of the nervous and other 
diseases which it produces may be inherited in some form 
or other by innocent children, who will be weak in mind 
and body from this cause. One of the leading physicians 
of England not long since stated as a fact that in the hos- 
pital which he attended seven out of every ten cases of 
sickness were caused by drinking alcohol. 

Effect of Tobacco and Opium on Digestion. — Many 
persons indulge in the use of tobacco, either smoking 
cigars, and thus taking the poisonous weed into their 
lungs with every breath, or chewing it in solid pieces, 



DIGESTION. 59 

In both these ways, as well as in the old practice of 
snuffing it up the nose, it is positively injurious to the 
system. It disturbs the stomach and produces vomiting 
and giddiness, and also affects the brain and the heart. 
The Government found that the cadets at West Point 
and Annapolis, who were at school there studying to 
enter the army and navy, were so much injured by 
using tobacco that it passed a law that all those chew- 
ing or smoking it should be severely punished. After 
using tobacco there is less appetite for food, and some- 
times disease of the mouth and throat. 

Some persons use opium and other articles of the kind 
to give them rest or to make them sleep, or because they 
think that such substances afford them some sort of pleas- 
urable feeling. All such articles should be strictly forbid- 
den. Their use does not produce healthy sleep, and the 
stomach or heart or brain will be greatly disturbed in 
their action. After the opium habit, as it is called, is 
once formed, the person cannot do without it. Opium 
takes away the appetite and checks the muscular action 
of the stomach and bowels. It should never be taken 
without the order of a physician. 

When we come to study the physiology of the heart 
and lungs and brain, we shall learn how injurious alco- 
hol and tobacco and opium are in their effect on those 
important organs. 

Tea and Coffee. — These articles are used as drink by 
the people of almost every nation. Tea was first used in 
England more than two hundred years ago. In modera- 
tion tea and coffee may assist the work of digestion and 



60 ELEMENTARY PHYSIOLOGY. 

satisfy the stomach, and thus prevent the person from 
taking anything stronger, such as whisky or brandy or 
beer, into the stomach. When they injure the stomach 
or the nervous system, it is because the tea or coffee is 
made too strong or taken in too large a quantity, or be- 
cause from some peculiarity of the person taking them 
these articles do not agree. A cup of tea or coffee should 
be made by placing a small quantity of either in boiling 
water for a few moments, but the mixture itself should 
not be boiled. 

Tea has a good deal of tannic acid in it, and this has 
the effect of checking the action of the stomach and bow- 
els. Taken in excess, tea may weaken the action of the 
iieart. Coffee, taken very strong, may produce disagree- 
able feelings of fulness in the head, and indigestion. 
Milk is the best food for children ; they will grow 
strong and healthy from its use, without using either 
tea or coffee. 

Quantity of Food to be Taken. — It is hard to say ex- 
actly what is the proper quantity of food for any one 
to take at a meal or in the course of the day. Every- 
thing must depend upon the age and health of the per-= 
son, and whether he is living in a warm or a cold climate. 
A strong man can take more food than a weak or old 
person or a young child. Eating too much is a common 
cause of sickness, especially with children. If the food 
should be swallowed too rapidly, the stomach will have 
too much work to do to get it ready for the good purposes 
it will serve afterward. 

The usual quantity eaten every day by a grown person 



DIGESTION. 61 

in full health is said to be half a pound to a pound of 
meat, about a pound of bread, about a quarter pound 
of fat, and between three and four pints of water, either 
taken as such or in the form of milk, tea, or other fluids. 
A larger amount is eaten in cold than warm climates, 
and in cold seasons of the year than in hot. The daily 
amount of food taken by an Esquimaux is said to be 
twelve to fifteen pounds of meat, besides a large mass of 
fat ; but this is because the climate is so very cold that 
he has to eat plenty of meat and fat to keep himself 
warm. A Russian admiral who was in the Arctic re- 
gions says that he saw a man eat twenty-eight pounds of 
boiled rice and butter at a single meal. One of the Arc- 
tic explorers saw an Esquimaux who in twenty-four hours 
devoured thirty-five pounds of meat, in addition to a 
number of tallow candles. 

Children need plenty of food, because they are always 
growing and taking exercise ; and it is a well-known fact 
that those who take exercise need much more food than 
those who do not. Meals should be regular and far 
enough apart to allow of full digestion being completed. 
Some persons require much more time than others, but 
scarcely any more than four or five hours between meals. 
Children can eat more frequently than grown persons, 
but the quantity at each meal should be moderate, not 
excessive, so that the stomach will not have too much to 
do. Supper should be light, and, as a rule, without meats 
of any kind, especially in the case of children, as a full 
supper eaten before going to bed is apt to disturb the 
brain and cause dreams or restlessness. 



62 ELEMENTARY PHYSIOLGY. 

Change in the kind of food is desirable. The strong 
require a different kind from the weak, and those who 
are engaged in heavy and fatiguing labor should eat more 
food and of a better kind than those who have to sit at 
their desks. Delicate persons and those with weak stom- 
achs should eat only such articles as are easily digested, 
and in small quantities frequently repeated. Bread and 
milk, a small quantity of meat and of vegetable food 
with fruits, form a good diet for such persons. As will 
be hereafter stated, food should not be swallowed in a 
hurry, as the action of the teeth in dividing the food, and 
of the fluids of the mouth in softening it, will not then 
take place. 

Hunger and Thirst. — After the stomach has been empty 
for a while — that is, after the person has not eaten for 
several hours — he begins to feel hungry. This is because 
the body needs food, and the feeling of hunger, as it is 
called, is the way in which our bodies tell us they need 
something to eat. If no food be taken, the different tis- 
sues will gradually break down, and the body will have 
to feed on itself. This condition could not last long, for, 
like the steam-engine, the body must have fuel or it will 
soon stop working. Even the vegetable seems to get 
hungry sometimes, for it sends out its little roots in alj 
directions in search of food. 

The feeling of hunger, or the desire for solid food, 
seems to come from the stomach, but when we get thirsty 
the feeling comes from the throat, and is an evidence that 
we want more water in our bodies. We have to drink a 
certain quantity of water every day in some form or 



DIGESTION. 63 

other, either as pure water or as tea or coffee or milk. 
We can live longer on water alone than on any dry food 
without water. 

Hints about Eating. — No more food should be eaten 
than is necessary to satisfy the appetite. It should not 
be eaten oftener than the wants of the body require, and 
this is usually shown by the feeling of hunger, or appe- 
tite. Three meals a day, five or six hours apart, are 
enough. The supper should be light ; the dinner should 
be the most nourishing, as more work, and therefore more 
loss to the system, has occurred. The food should be 
eaten slowly and be well chewed before swallowing. It 
is better not to overload the stomach, as that organ will 
soon get tired of being overworked. Water should not 
be taken in large quantities at meals, as it dilutes the 
food too much and weakens the power of the stomach. 
Alcoholic liquors in any shape should not be taken at 
meals or at any other times ; they do not add anything 
nourishing, nor do they help other things to be digested. 

For children vegetable foods are better than animal, 
because they do not have the same stimulating or excit- 
ing effect. Veal, pork, ham, fried meats, and pastry 
should be avoided by children ; they disagree with many 
grown persons. Hot biscuit, cakes, and pies should be 
avoided at night. Meals should be taken at regular 
hours, as the stomach needs regular work and regular 
rest. Exercise, work, or study should be avoided after 
a full meal ; the needs of the stomach require at that 
time that the blood and the powers of the body shall not 
be called away to do other work. Running, leaping, and 



64 ELEMENTARY PHYSIOLOGY. 

jumping rope should not be indulged in for at least two 
hours after a full meal. At meal-times the mind should 
be cheerful and free from care ; children should not hurry 
to their meals when flushed and excited or heated by play, 
but wait until their nerves get quieted down. 

The food should not be eaten too hot or too cold. Very 
hot drinks may injure the teeth or the stomach and delay 
digestion. Very cold food chills the stomach. Ice-cold 
water should not be taken into the stomach in any large 
quantity, especially when the body is heated. Such a 
freezing mixture as ice-cream, although very pleasant to 
the taste and cooling to the mouth and stomach, may in- 
jure the stomach from the sudden chilling received by 
that organ. It should therefore be eaten slowly. Spiced 
food, pepper, mustard, sauces, pickles, and horseradish may 
disagree with the stomach by exciting it so much that in 
time that organ gets tired of the constant stimulation, and 
may become mucii weakened in its action. 

Organs of Digestion. — The simplest arrangement for 
digestion is that of the vegetable, which obtains its food 
from the earth. It has no other organs, such as a stom- 
ach, but the water or other matter from the earth passes 
directly into it. In some of the lowest and smallest 
forms of life the whole animal is a sort of sac, or bag, 
with only one opening, and looks like a delicate gum- 
bottle. The animal is all stomach, and like a thin rub- 
ber bottle can be turned inside out. In some fluids there 
are little living bodies which are so small that they can 
only be seen with a microscope, and yet in them there is 
a body having an opening for food, a part like a stomach, 



DIGESTION. 65 

with an open tube or canal leading from it. The organs 
of digestion are most perfect in man and the higher classes 
of animals, and in them we find a cavity or a number of 
cavities in which the nutritious portion of the food is 
prepared, and the useless portions of food are expelled. 

In man the arrangement for digestion consists of a 
long tube or canal, varying greatly at different parts in 
size and structure. It is usually divided into the follow- 
ing parts : mouth, pharynx, oesophagus or gullet, stom- 
ach, and bowels or intestines. The stomach and bowels 
occupy the greater portion of the abdo'men, as the cavity 
is called (Fig. 25), and are the chief organs of digestion. 

The Mouth. — The mouth receives the food taken into 
it; the teeth cut and crush it; the tongue and cheeks 
move it around and around, while the mouth pours out 
a thin fluid which softens it. 

The Teeth. — The teeth are made up of a very hard 
material called the ivory or dent'ine, and they are inserted 
deeply into the jaw by roots. The part of the tooth 
above the gum is called the crown, which is covered by a 
thin layer of material called enam'el; and this is the 
hardest substance in the body. Inside the tooth is a 
cavity containing nerves and blood-vessels. 

When a child is born it seems to have no teeth, but 
many of them are already in the jaw, but have not risen 
to the surface of the gum. When a young child gets its 
first full set of small teeth it should have twenty alto- 
gether. These are called temporary teeth (Fig. 16), be- 
cause they do not stay in the jaw all through life ; and 
they are called milk teeth, because most of them come at 



66 



ELEMENTARY PHYSIOLOGY. 



a time of life when the child is living entirely upon 
milk. When the child gets to be about six or seven 




Opening for passage of nerves and blood-vessels. 

Fig. 15. — General View of the Teeth, the bone being divided to show 
this more clearly. 

years old the roots of the milk teeth become absorbed, 
and the teeth are ready to fall out. Then the perma- 
nent teeth come and take their places, and these stay in 



DIGESTION. 



67 



the mouth during all the rest of life unless they become 
lost by disease or decay. There are thirty-two perma- 
nent teeth, sixteen in each jaw. 

The smaller sharp teeth seen in Fig. 15 are intended 
for cutting and dividing the food, the large ones for 
grinding or mashing it. The permanent teeth are devel- 




Fig. 16. — Milk Teeth and Permanent Teeth as found in the Jaw at 
the same Time. 

1' to 5' are milk teeth ; 1" to 8" are permanent teeth. 



oped in the jaw below the milk teeth, and both are found 
in the jaw at the same time, about the fifth year of age 
(Fig. 16). They gradually push out the milk teeth from 
that time of life until the twelfth or fourteenth year of 
age. The " wisdom tooth," so called on account of its 



68 



ELEMENTARY PHYSIOLOGY. 



not making its appearance until the twentieth or twenty- 
first year of life — when a young person is supposed to be 
wiser than during his younger years — is the third large 
tooth of each jaw. 

The teeth are of such shape in various animals as to 
be adapted to the special food on which they live. The 
sharper teeth in front are called inci'sors from their 
cutting properties, and canine because they are like 
those of the dog. The largest teeth are called molars, 
from a Latin word meaning a a mill," because they grind 
the food as a mill would. The motions of the jaw^ also 
admit of a cutting or crushing action upon the food. In 
animals which live entirely on animal food the jaws are 
very strong, and move more readily up and down than 
from side to side. The muscles of the jaw r are also very 
strong, and the cutting teeth are much more powerful 
than those for crushing, the latter being sharper than in 
other animals. By looking at a tooth we can usually 
know at once the kind of animal, and some learned men 
have been able to decide from a single tooth exactly 
what the rest of the animal must have looked like, 

although the kind of animal 
may have long since ceased 
to exist upon the earth in 
any part of it, for each an- 
imal is formed by Nature on 
a general plan or system. 

Some animals feed en- 
tirely on flesh, some on in- 
others on grass. Man has 




Fig. 17.- 



-Teeth of Insect-eating 
Animal. 



sects, and some on grain, 



DIGESTION. 



69 




Fig. 18. — Teeeh of 
Fruit-eating An- 
imal. 




teeth and digestive organs adapted to all kinds of food, 
whether animal or vegetable. Animals which feed en- 
tirely on insects have conical or sharp-pointed teeth 
which fit closely into one another in 
the two jaws like the teeth of clock- 
work (Fig. 17). Those animals which 
live mainly on fruits have the teeth 
rounded rather than sharp (Fig. 18). 
Grain-eating animals, whose food re- 
quires crushing or bruising rather than 
cutting, have large flat teeth, which, like millstones, crush 
and break up the food into fine 
particles by the side-to-side move- 
ment of the jaws (Fig. 19). In 
the flesh-eating animal (Fig. 20) FlG - 19 -— Teeth of Grain- 

,, t ;1 t eating Animal. 

the large teeth or molars are 

sharper, and so placed as to meet like scissors-blades, 
while the front or canine 
teeth are very large. The 
sharp front incisor teeth in 
other animals become in 
the horse more like grind- 
ers or molars in structure and 
shape. A number of animals 
have grinding or molar teeth FlG - 20.— Teeth of Flesh-eating 
in some form or other. The 

teeth of the elephant are entirely of this kind. Some 
animals, as the whale, have not any teeth. Of the thirty- 
two teeth of man, twelve are like those of the flesh-eating 
animals, and twenty like those of grass-eating animals. 




70 



ELEMENTARY PHYSIOLOGY. 



The movement of his jaws is upward and downward 
and sideways. 

The Tongue. — The tongue moves the particles of food 
around in the mouth, to be acted upon by the various juices 
or fluids poured into it. Some of the lower animals seize 
their prey with the tongue. While man uses his hands to 
convey food to his mouth, the elephant has a long snout 




Fig. 21. — Salivary Glands. 

1, parotid gland; 2, sublingual gland; 3, submaxillary gland; a, nerve; c, d, e, 
muscles of the face and neck ; /, lower jaw ; g, artery. 



called the trunk, through which it can suck articles into 
its mouth. Insects have feelers around the mouth for 



DIGESTION. 



71 



similar purposes. In some animals the motion of the 
tongue in the mouth enables them to suck in liquid 
food. 

The Salivary Glands. — These glands (Fig. 21) are 
found on each side of the mouth in man, and are three 
in number. They pour out a thin and a thicker kind 
of fluid, which becomes mixed with that from the mem- 
brane lining the mouth. Although this fluid, called 
sali'va, is being constantly formed and swallowed, the 
presence of food in the mouth excites these glands, and 
an additional quantity of saliva flows into it. Even 
the mere sight of agreeable 
food has this effect, which 
is well known as "mouth- 
watering." 

The amount of saliva 
poured out varies with the 
kind of food ; if it is hard 
or dry a larger quantity is 
poured out. The saliva soft- 
ens and moistens the food, FlG - 22.— Structure of a Sali- 

T .« n n t t VARY GLA.ND. 

and it the food has any 

starchy matter in it, it is changed by the saliva into a 
gummy substance called dex'trm, and afterward into 
grape-sugar. This, being soluble, is more easily ab- 
sorbed. Perfect division of the food, and perfect mix- 
ture of saliva with it, are necessary to ensure perfect 
digestion in the stomach. 

The salivary glands, when examined under the micro- 
scope, resemble a bunch of grapes (Fig. 22). The average 




72 ELEMENTARY PHYSIOLOGY. 

amount of saliva poured into the mouth in the course of 
twenty-four hours has been estimated at from two to 
three pounds. The terms parot'id, submaxillary, and 
sublingual, applied to the salivary glands, merely mean, 
from their Greek and Latin origin, that they are near 
the ear, under the jaw, or under the tongue, as will be 
seen in Fig. 21. 

Swallowing the Food. — When the food has undergone 
these processes in the mouth it is swallowed. Swallow- 
ing, or deglutit ff ion, as it is technically called, includes 
the passage of the mass of food from the back part of 
the mouth into the stomach, and requires the action of 
the mouth, throat or phar'ynx, as it is called, and a tube 
called the oesophagus or gullet, which passes directly 
into the stomach. 

The pharynx and oesophagus together form a muscular 
tube or canal extending from the mouth to the stomach 
(Figs. 23, 24). The cavities of the mouth, nose, and 
larynx, or upper part of the air-passages, open into the 
pharynx (Fig. 24). The oesophagus (Fig. 23) is about 
nine inches long, and, like the pharynx, is lined with 
a smooth membrane called a mucous membrane, which 
pours out a thin fluid called mucus to keep it moist. 
It also has a muscular coat which keeps the tube con- 
tracting, so that the food is moved onward toward the 
stomach. 

The first part of the act of swallowing is under the 
control of the will, but the passage of the food from the 
throat to the stomach is entirely beyond our control. 
This is a wise provision, for otherwise the particles swal- 



DIGESTION. 



73 



lowed might pass into the upper opening of the air-pas- 
sages, as they occasionally do when, in common language, 
they u go the wrong way/' During the act of swallow- 



Gall-bladder 



Large intestine 



Appendix 




Spleen. 



Small intestine. 
Large intestine. 



Small intestine. 
Fig. 23. — The Organs op Digestion. 

ing the upper part of the air-passages is raised by the 
muscles connected with it out of the way of the mass of 
food. The passage from the back part of the throat into 




Fig. 24. — General View of the Mouth, Pharynx, etc. 



1, canal from throat to middle ear ; 2, back part of nose ; 3, soft palate ; 4, soft 
palate covering tonsil; 5, tonsil; 6, base of tongue; 7, epiglottis ; 8, part of 
cartilage of larynx ; 9, pharynx ; 10, cavity of larynx ; 11, nasal fossae ; 12, 
vault of the palate, or roof of mouth; 13, 14, tongue; 15, muscle beneath 
tongue ; 16, hyoid bone ; 17, interior of larynx ; 18, 19, thyroid cartilage. 



DIGESTION. 75 

the nose is also closed, so that fluids cannot get into that 
cavity. 

There is a cartilaginous body called the epiglottis 
(meaning "upon the glottis") which is placed behind the 
base of the tongue, and when the food is swallowed it 
covers the glottis, as the opening in the larnyx is called, 
and thus aids in preventing the mass from getting into 
the air-passages. When the muscles of the lower part 
of the oesophagus contract, they force the food into the 
stomach. The lower part of the oesophagus remains con- 
tracted for a while after the entrance of the food into the 
stomach, so as to prevent its return upward. 

The Process of Digestion. — The first step of digestion 
is the taking of solid or liquid food into the mouth. 
Digestion in the mouth includes the action of the salivary 
glands, the teeth, etc., already described. Deglutition, 
or swallowing, is the next step, after which come, in im- 
mediate succession, digestion in the stomach and bowels. 

When the food is hastily swallowed — and this is gener- 
ally called " bolting the food " — the cutting and crushing 
action of the teeth does not take place, and the food passes 
into the stomach in a state unfitted for perfect digestion, 
so that dyspepsia or indigestion, as it is called, may result, 
especially if this neglect becomes a matter of habit. In 
the act of drinking, fluids are usually sucked into the 
mouth and swallowed without any action upon them 
in that cavity. They are acted upon in the stomach. 
When the lips are applied to a cup, the air is drawn 
inward by inspiring or breathing in, and the liquid 
flows into the mouth. 



76 



ELEMENTARY PHYSIOLOGY. 



Digestion in the Stomach and Intestines. — When the 
food reaches the stomach it is subjected to entirely new 
action. Here it remains for a greater or less time accord- 
ing to its digestibility. The stomach and bowels of man 
are of such a length and arranged in such a way that all 

kinds of food taken into 
them can be digested. Flesh- 
eating animals do not require 
a long canal or a complicated 
stomach, as the food they eat 
is easily digested. Grass- 
eating animals require a long 
canal and plenty of room in 
the stomach for digestion, as 
the food is not easily digested. 
Some of these animals, there- 
fore, have four stomachs. 

In man the stomach is the 
largest single part of the ca- 
nal, and is in shape like the 
ordinary bagpipe. It lies 
across the upper part of the 
abdomen, and is separated 
from the chest, or thorax, in 
which the heart and lungs 
are placed, by a thick mus- 
cle, called the dVaphragm 
(meaning a partition) (Fig. 25), which covers the whole 
width of the floor of the chest. 

The opening in the stomach at its left end (Fig. 26) is 




Fig. 25. — The Thorax and 

Abdomen. 

1, thorax, or cavity for heart and 
lungs ; 2, diaphragm ; 3, abdomen ; 
4, spinal column ; o, spinal canal. 



DIGESTION. 



77 



for the entrance of the oesophagus. It is opened and 
closed by muscles. The opening at the right side is the 
point at which the food passes into the intestine, or bowel, 
which here begins its course. The left end of the stomach 
is the card'iac extremity (meaning " near the heart"); 
the other, the pylo'ric extremity (from pylorus, "a jani- 




Fig. 26. — Interior of the Stomach. 

P, pylorus, or right end of the stomach ; E, oesophagus ; C, cardiac orifice, at the 
left end of the stomach. 



tor"), because a kind of valve is found here which, acting 
like a janitor or gatekeeper, will usually stop the food from 
passing into the intestine until it is properly prepared to 
do so. The stomach is lined by a membrane (Fig. 26) 
which pours out mucus, and is hence called a mucous 
membrane ; and this is continuous from the inner edge 
of the lips through the whole tube or alimentary canal, 



78 



ELEMENTARY PHYSIOLOGY. 



as it is called. This mucus keeps the membrane always 
moist, and is the only fluid poured out when the stomach 
is empty. 

When any article of food passes into the stomach a 
peculiar colorless fluid is poured into the interior of that 
organ, which is called the yas'tric juice. It is chiefly 

water, but contains 
an acid and a fer- 
ment to which the 
name pep' sin has 
been given. The in- 
ternal surface of the 
stomach presents a 
network or honey- 
comb of very small 
ridges, in the spaces 
between which the 
mouths of little 
glands open. Very 
many blood-vessels 
enter these ridges and send numerous little branches or 
vessels around these glands. Many little glands are 
found in all parts of the stomach, but especially at the 
upper part. They pour out a thin fluid, and add to the 
moisture of the stomach. There is always fluid pres- 
ent, but the gastric juice, so called, is probably poured 
out in larger quantity in that part of the stomach lying 
next to the bowel, and only after food is taken. These 
glands (Fig. 28) are found more at the lower part of 
the organ. 




l 

Fig. 27. 

1, 2, 3, pits in mucous membrane of stomach ; 

4, 5, orifices of the glands. 



DIGESTION. 



79 



The muscular coat of the stomach 
(Fig. 29) is outside the mucous one, 
but in contact with it. The contrac- 
tions of the stomach, which produce 
the churning movement in digestion, 
are due to the presence of the mus- 
cular coat, which is made up of fibres 
running in different directions. Some 
of these fibres run the whole length 
of the stomach, some run around it, 
others cross it at an angle. The effect 
is to contract the stomach in every 
direction. Should all these fibres con- 
tract at the same time, the stomach 
would be emptied and the food ex- 
pelled from it forcibly. One set of fibres, acting alone, 




Fig. 28. — Gland from 
Pyloric Portion of 
Stomach (magnified). 

1, duct or canal ; 2, prin- 
cipal branches; 3, end 
portion. 




Fig. 29. — Muscular Fibres of the Stomach. 
1, circular fibres; 2, oblique fibres. 



80 



ELEMENTARY PHYSIOLOGY. 




contracts or shortens the stomach ; another set presses on 
the contents of the stomach, and causes the food to pass 
from one end to the other. The ob- 
lique fibres when they contract change 
the shape of the stomach (Fig. 30), so 
that the organ is divided into two dis- 
tinct portions. 

The outer coat of the stomach, the 
serous, is a delicate membrane, which 
is not concerned in digestion. 
Stomachs of Other Animals. — In man the stomach is 
not as small as in the flesh-eating animal. In the herb- 
eating animal the stomach is very complicated. In the 



(Esophagus, 



(Esophageal, 
groove. 



Fig. 30. — Showing 
Contraction of 
Muscles of the 
Stomach. 



Many plies, or. 
3d stomach. 



Intestine 




Paunch, or 1st 
stomach. 



Fig. 31. — Stomachs of a Sheep (Outside View). 

ox, for example, there are four distinct divisions, all of 
which are concerned in the process of digestion, but of 
which the fourth is the only one like the human stomach. 
Some of these animals have the power of returning the 



DIGESTION. 81 

food from the second stomach to the mouth, to be nomi- 
nated, as it is called, or chewed over again ; and when it 
comes down again it passes directly into the third stom- 
ach without entering the first and second. The peculiar 
arrangement of a sheep's stomach is shown in Figs. 
31, 32. 

In birds, in which grain or seed is swallowed whole, a 
sac or bag called a crop (Fig. 33) exists, in which fluid is 

(Esophagus V I ^^___ — ^^^ 

(Esophageal groove l\# ' ""'•* * • 

Re ^ et — %Mn w^^w 

i' | & 

O 3 3 

Fig. 32. — Stomachs of a Sheep (Inside View). 

poured out to aid digestion. There is also another small 
cavity or second stomach, which leads into a third stom- 
ach or gizzard, a kind of paunch connected with the 
alimentary canal proper. This organ is made up of 
powerful muscles forming a thick sac with a small cav- 
ity, which may contain pebbles swallowed by the bird, 
that act like teeth and by their millstone action crush the 
food. In flesh-eating birds the gizzard is not so powerful, 
and the whole canal is much more simple, as the food 
does not require so much digestion. In some of them 
6 



82 



ELEMENTARY PHYSIOLOGY. 



the stomach is merely a sac of muscles and membranes, 
and pours out a fluid which helps to digest the food. 



Gizzard 



Pancreas 



Small intestine- 
Large intestine- 
Large intestine 




Liver. 

.. Gall-bladder. 
Bile-ducts. 



Fig. 33. — Digestive Organs of Domestic Fowl. 

This is the more necessary as the animal does not pos- 
sess any teeth for chewing, and the digestive organs are 
packed away in a small space so that its flight will not 
be interfered with. 



DIGESTION. 



83 



In reptiles, a class of animals which is capable of ab- 
staining from food for a long time, there is generally a 
large mouth, with teeth that form part of the jaw itself, 
or are inserted in sockets ; or, like tortoises, their jaws 
are horny. The intestines are usually short. 

Those fishes which feed on the blood and juices sucked 
from other animals have their mouth, teeth, and tongue 
arranged on the principle of the cupping apparatus of the 




Fig. 34. — Digestive Organs of Insects. 

A, Mole Cricket: a, head and appendages; b, salivary glands; c, secreting 

granules of the same glands ; d, feelers ; e, cardiac part of stomach ; /, ac- 
cessory pouches of the stomach ; #, middle part of stomach ; A, pyloric part 
of stomach ; i, intestines ; k, canals representing liver. 

B, Bee : a, head and mouth ; b, salivary glands ; c, oesophagus ; e, crop ; h, stom- 

ach j fc, canals representing liver. 

surgeon. In all the liver is large, and digestion is per- 
formed quite rapidly. 

Some insects (Fig. 34) feed on the juices, others on the 



i 



84 ELEMENTARY PHYSIOLOGY. 

solid parts, of plants and animals. The grasshopper has 
a cutting arrangement to cut the food, in addition to feel- 
ers, a tongue, etc. In grass-eating insects the digestive 
organs are quite complicated. There are really three 
stomachs — a crop, gizzard, and stomach proper. The 
canal, including the intestines, is not straight, but gen- 
erally winding, with enlargements and contractions at 
various points. In insects which live chiefly on animal 
food the canal is short, and in those which feed on veg- 
etable substances the canal is longer. This we have 
already seen to be true of animals much higher in the 




b 



C 

Fig. 35. — Stomachs of Various Animals. 

A, sheep ; B, hysena ; C, marmot ; D, seal ; E, salmon, a, cardiac opening of 
stomach ; 5, beginning of intestine. 

scale. Such wonderful plans and systems are further 
indications of the wisdom and far-seeing knowledge of 
the Almighty. 

The variety of forms of stomach peculiar to different 
types of animals is well shown in Fig. 35. 

Action of the Stomach in Digestion. — When the food 
enters the stomach, that organ becomes gradually swollen, 
especially in its muscular coat, so as to occupy a much 
greater space in the abdomen, and rotates or turns partly 



DIGESTION. 85 

upon itself. When too much food is taken into the 
stomach, it may press upward against the floor of the 
chest, so as to seem like a weight against it in breath- 
ing. The presence of food in the stomach causes the 
muscles of that organ to go on regularly contracting 
and relaxing, as muscles always will do when they are 
excited. The food thus gets thoroughly mixed with the 
fluids in the stomach by regular churning movements. 
When the diaphragm, the large muscle separating the 
chest from the abdomen (Figs. 25, 45), contracts, it also 
presses upon the food in the stomach. 

Digestion in the stomach may therefore be said to in- 
clude the churning motion of the «>rgan and the mixing 
of the food with its fluids. 

Changes in the Food in Digestion. — The soft, pulpy 
mass in the stomach is no longer the food proper, but 
food mixed with fluids from the salivary glands and the 
stomach. Saliva is probably poured into the stomach 
from the mouth during the whole time that the food is 
being digested in the stomach. If the food taken has 
been starchy, some of it has been changed into sugar in 
the mouth ; but some of it that passed down into the 
stomach without being changed will be acted upon by 
the saliva in the stomach. Fatty matters are digested 
after they leave the stomach and pass into the intestine. 

Albuminous, fibrinous, and other matters of the kind, 
such as those of which meat is composed, are digested in 
the stomach. All matters that are not digested, and are 
of no use to the body, pass down into the large intestine. 
Oily and fatty matters — and, as a rule, vegetable food — * 



86 ELEMENTARY PHYSIOLOGY. 

are digested in the upper part of the bowel. Thick 
fluids, such as soups, may be acted upon in both the 
stomach and bowel. 

Animal food is more digestible than vegetable. Bread, 
potatoes, and pastry are partly digested in the stomach 
and partly in the intestine. Thin liquids, such as water, 
alcoholic drinks, etc., as will be shown hereafter, are gen- 
erally absorbed by the blood-vessels of the stomach at 
once, without being digested. 

The length of time which food spends in the stomach in 
being digested is two to four hours, but longer than this 
in those who do not take the proper amount of exercise. 
Boiled rice only remains one hour ; fried veal, about four 
hours and a half. While the food is in the stomach it is 
exposed to a temperature of at least 100° Fahr. The 
gastric juice, acids, heat, etc., all acting together, change 
the animal food into another form of albumen, called 
pep'tone or albu'minose, which is more easily absorbed 
than albumen. The active principle of the gastric juice, 
pepsin, is the ferment by means of which the changes in 
the food are effected. 

Thin fluids, after being swallowed, enter the stomach 
without being changed in any way in the mouth, and are 
rapidly absorbed by the veins of the stomach without 
undergoing any other action, and by the veins of the 
small intestine. The veins into which they enter unite 
with other veins to go directly to the liver. After a 
short stay there this blood passes into the current of the 
blood to the heart, and so on all through the body. This 
is why the effect of alcohol is so soon felt when taken 



DIGESTION. 87 

into the stomach, and why the liver becomes diseased in 
those who drink liquor to excess. 

Digestibility of Food. — Substances are said to be easy of 
digestion if they are know r n to make but a short stay in 
the stomach ; but some of these very articles may not be 
nourishing. It seems to be the rule that those articles of 
food which are most nourishing do not pass out of the 
stomach very rapidly. It seems as if that organ had the 
power or sense of choosing what is best for it. Milk 
probably disappears from the stomach very rapidly. It 
is said by one writer that an hour after it is swallowed 
there are scarcely any traces of it in the stomach ; but 
milk is composed not only of sugar, water, and salts, all 
of which may be absorbed in that time, but it also has in 
it fatty matter, which is not so easily gotten rid of. Some 
writers say that five or six pounds of gastric juice are 
poured out into the stomach every day — ten or twelve 
pounds, according to others. 

Over-exertion of any kind should be avoided soon 
after taking a full meal. It is well not to lie down soon 
after eating, or to take a long sleep at such a time, or to 
bend over a desk to study or write in such a way that 
the stomach will have its contents pressed upon too much. 
A short nap may be taken in a sitting position. The di- 
gestive powers of young persons are better than those of 
adults, considering the food which they are each capable 
of taking. 

Some persons take little or no drink at meal-times. It 
is certainly wrong to wash down every portion of solid 
food with liquids, as is the habit of some. A small 



88 ELEMENTARY PHYSIOLOGY. 

quantity of liquid may be taken, and after the gastric 
juice has ceased to act it may be excited to renewed action 
by a fresh supply of water. Some persons take a glass of 
pure water in the morning before breakfast. Exercise 
before breakfast disagrees with many weak stomachs. 

Digestion in the Intestines. — The bowels or intestines 
are a continuous tube or canal leading directly from the 




Fig. 36. — General View of the Intestines. 

1, 2, 4, small intestine; 3, 6, 7, large intestine; 5 appendix; 8, stomach: 

9, diaphragm (cut). 

stomach. They vary in length in different animals, and 
are usually divided into the small and large intestines. 
The small intestine (Fig. 36) is a narrow tube about 
twenty feet long, coiled upon itself. It is in this portion 
of the tube that intestinal digestion chiefly takes place. 



DIGESTION. 



89 



The large intestine is intended rather as a receptacle 
for the useless and undigested portions of the food. The 
intestines have similar coats to the other parts of the 




Fig. 37. — The Large Intestine (opened). 

1, 2, 3, small intestine, connecting with large intestine by a valve 6 ; 4, 5, 8, 

large intestine ; 7, appendix. 

canal, being lined with mucous membrane, which is cov- 
ered by a muscular coat, and this again by a thin serous 
coat. The intestine has a worm-like movement of con- 



90 ELEMENTARY PHYSIOLOGY. 

traction and dilatation like that of the stomach, and this 
is excited by the presence of food. 

Intestines of Other Animals. — The arrangement of the 
intestines in the lower animals differs from that of man. 
In the latter there is a small pouch connected with the 
intestine, called the appen f dix y (Fig. 23), of no known use 
whatever, but it seems to be left there to show that man 
is in some respects like the other animals in structure. 
In some animals it is so large as to be really a distinct 
intestine. In birds that eat grain or that feed on all 
kinds of food a portion of the intestine is double. In 
reptiles the intestines are short, and there is but little 
difference in size between the large and small intestines. 
In insects the intestinal canal is often more complicated 
than in some of the upper classes of animals. 

Intestinal Juices. — In man the mucous membrane of 
the intestines is thrown into folds, and on this membrane 
is poured, from an immense number of little bodies or 
glands, a fluid called the intestinal juice. At a distance 
of four or five fingers' breadths from the pylorus, the 
opening which is at the right end of the stomach, two 
canals or tubes open into the intestine, which bring bile 
from the liver and gall-bladder, and a fluid called the 
pancreat'ic juice from an organ called the pan'creas, or 
abdominal sweetbread, as it is sometimes called, lying 
close to the stomach (Fig. 38). Both of these fluids aid 
in the digestion of the food in that portion of the intes- 
tine. 

It has been estimated that at least twenty pounds of 
fluids useful in digestion are poured out in the twenty- 



DIGESTION. 



91 



four hours: Saliva, 3 J pounds; bile, 3J; gastric juice, 12 ; 
pancreatic juice, J pound ; and intestinal juice, J pound. 
AVhen the valve between the stomach and intestine, 
which we have stated is called the pylo'rus, or gatekeeper, 
allows the food to pass, after digestion in the stomach has 




Fig. 38. — The Pancreas. 

Divided, so as to show — 1, pancreatic duct or canal ; 2, canal emptying 

into the intestine 3. 

taken place, the muscles of the stomach drive it out into 
the first part of the intestine. Here the, food is mixed 
with the bile and pancreatic juice, and with the intestinal 
juice already referred to. 

When the pancreatic fluid is mixed with the food the 
mixture looks like what the apothecary calls an emulsion, 
for an emulsion is nothing but an oily or fatty matter, 
with something else that keeps it w r ell mixed, and it is 
more easily absorbed for useful purposes in the body e 
Besides this, the starchy parts of the food that were not 
changed into sugar in the mouth are here changed by the 
action of the pancreatic juice. This fluid also has some 
action on albuminous matters like that exerted by the 
gastric juice. 



92 ELEMENTARY PHYSIOLOGY. 

The bile is secreted by the liver, an organ lying under 
the diaphragm, above the stomach (Fig. 23); a very large 
organ, weighing three or four pounds and measuring 
ten or twelve inches in width. Only a small part of the 
bile formed by it and poured into the intestine is of use 
in digestion ; the rest of it passes along with the refuse 
food. Bile is one of the chief agents in the digestion of 
fats. 

There is a sac connected with the liver called the gall- 
bladder (Fig. 23), and this receives the bile from the 
liver. This is afterward poured both from the liver and 
gall-bladder into the intestine. While food is being di- 
gested in the stomach the bile from the gall-bladder, as 
if by a telegraphic signal from the stomach, begins to 
come down into the intestine, to be ready for its duty 
when the food arrives. 

By the time the food has reached the large intestine 
all the matter that is likely to be of use to the body has 
been taken from it. Digestion proper may be said, 
therefore, to be almost ended with the small intestine. 
Nearly all the food taken into the mouth is digested in 
one form or another. 

To sum up, we may briefly say that when solid food 
is taken it is disposed of as follows : 

The starchy matters are converted in the mouth and 
stomach, by the action of the saliva, into sugar, and also 
by the pancreatic juice in the small intestine. 

The fatty matters are chiefly digested in the small in- 
testine by the pancreatic juice and bile together, being 
made into an emulsion for easy absorption. 



DIGESTION. 



93 



Albuminous matters, such as meat, are acted upon by 
the fluids of the stomach. 




Villi. 



Glands. 



Areolar tis- 
sue. 

Circular mus- 
cular fibres. 

Longitudinal 
muscular 
fibres. 




Fig. 39. — Section of the 
Small Intestine, as seen 
under the microscope, 

SHOWING THE VlLLI. 



b c b 

Fig. 40. — One of the 
Villi of the Intes- 
tine, as seen under 
the Microscope. 

a, layer of cells ; 6, blood- 
vessels ; c, commence- 
ment of vessel contain- 
ing chyle. 



How the Food is Absorbed. — The worm-like action of 
the intestines passes the food slowly onward from one por- 
tion to another. The mixture of intestinal fluids with food 
forms a milky fluid called chyle (pron. kile, from a Greek 
word meaning "juice"). In the folds of the mucous 
membrane of the intestine may be found a series of ves- 
sels which absorb this milky fluid and carry it to be 
emptied directly into the blood. 

There are delicate elevations on the surface of the mu- 
cous membrane of the intestine which are called villi, so 
closely placed together as to give it the appearance of fine 
velvet. (Fig. 39 shows how these villi look when they 
are very largely magnified under the microscope.) In 



94 



ELEMENTARY PHYSIOLOGY. 



each villus is a network of small blood-vessels carrying 
the milky fluid just referred to, called chyle. When we 
examine one of these villi under the microscope, we find 
the appearance seen in Fig. 40. The cells on the outside 



.s« 


c3 cc 


O 3 


,CO 


Ojr^ 


P«3 


°Z 


a -a 


A O 


K ao 


H 


tJ 




Chyle-bearing 
vessels. 

-Intestine. 



Fig. 41. — Lacteal or Chyle-bearing Vessels of the Intestine. 



of each villus come in contact with the food that has 
been already digested, and absorb it. 

After entering the vessels which carry the chyle 
(sometimes also called the lac'teals, from a Latin w T ord 
meaning " milk "), the chyle is emptied into a long canal 



DIGESTION. 



95 



which passes along the back part of the chest, in front 
of the spinal column, called the ihorac f, ic canal or duct 
(Figs. 41, 42). This carries the chyle up to the left 
side of the neck to empty it into one of the large 




Fig. 42. — Thoracic Duct and Chyle-bearing Vessels. 

1, 2, thoracic duct ; 3, termination in the vein ; 4, lymphatic glands ; 5, 6, veins 
of the right side. 

blood-vessels in that region. On the way between the 
intestine and the thoracic canal (Fig. 41) it passes 
through a number of small bodies called lymphat'ic 
(/lands (Figs. 41, 42), which produce changes upon it 
to render it more like the blood with which it is to 



96 



ELEMENTARY PHYSIOLOGY. 



be mixed. When once mixed with the blood, it passes 

with that fluid to the heart. 

To sum up, therefore, the ac- 
tion of absorption of liquid food, 
we may repeat that it is absorbed 
either, if very thin, through the 
blood-vessels of the stomach or 
intestine, passing directly to the 
liver, or by the lacteals and the 
thoracic duct to the veins of the 
neck. The chyle becomes more 
and more like the blood as it 
passes along with that fluid for 
the nourishment of the body. 
The chyle-bearing vessels ab- 
sorb fatty matters which we have 
shown are made into an emul- 
sion by the juices of the intes- 
tine, those albuminous matters 
which resulted from the action 
of the gastric juice on meats, 
and the portions of sugar which 
w T ere changed from starchy mat- 
ters. 

Lymphatics. — There is an- 
other set of fine vessels in al- 
most every part of the body 
which are busily engaged in 
absorbing the various materials 

collected from the wear and tear of the system. These 




Fig. 43. — Lymphatic Vessels 
on the Surface of the Arm. 



DIGESTION. 



97 



vessels are called lymphatics, because they carry a very 
thin fluid, called lymph, which has no color and is car- 
ried by these vessels (Figs. 43, 44) to be emptied into 
the blood. These lym- _ ^ 2 

phatic vessels are very 
numerous, and run 
into one another like 
streams into a river, 
gradually forming ves- 
sels of considerable 
size, which finally 
unite and either emp- 
ty into the thoracic 
duct, in front of and 
alongside the spinal 
column, or on the right 
side of the bodv into 
a large canal or tube 
called the right lym- 
phatic trunk. Both of 
these empty the lymph into the current of blood. These 
vessels have projections called valves, which prevent the 
lymph from flowing backward. 

This whole plan of vessels and glands is a system of 
drainage like that employed in some soils, in which the 
water drained from boggy lands forms channels, which 
unite to make larger streams, still increasing in size and 
occasionally expanding into pools, and at last pouring 
into a river or the ocean. 
7 




Fig. 44. — Deep Lymphatics of the Finger. 



1, 1, deep network of lymphatic vessels of the 
skin ; 2, 2, lymphatic trunks connected with 
these vessels. 



98 ELEMENTARY PHYSIOLOGY. 

QUESTIONS. 
Why does the body need food ? 

What is Digestion? Do vegetables have any digestion? 
What kinds of articles are used as food ? 
Why is food of a simple kind, such as milk, the best ? 
What fluid in the body is the milk like ? 
Why are different salts, such as table-salt, etc., used as food ? 
Why is iron important as an article of diet ? 

In what form do we use starch for food ? Sugar ? Fats ? Gums 1 
What is albumen ? What are albuminoid matters ? 
Where do we find fibrin and casein ? 
What is the use of fat in the body ? 
Why do we mix the different articles for food ? 
What is nitrogen ? What has it to do with the food ? 
Why is it important to eat a variety of articles of food ? 
What are some of the albuminous articles of food ? 
What portions of animals are used as food ? 
Why is very young meat not best for food ? 
What do we know about the meat of birds for food ? Of fish ? 
What is milk composed of? What becomes of it when swallowed? 
What is cream ? Butter ? Buttermilk ? Cheese ? 
What do you know of eggs as articles of food ? 
What is bread ? What effect has yeast upon it ? 
What are the different breads made from ? 
What are the effects of fruits? The best rule for eating them? 
What is the effect of cooking upon the food ? 
What is the best fluid for drinking ? 
How much water is there in the body ? 
How much water should we drink in a day ? 
What kinds of water are used for drinking purposes ? 
What are the alcoholic drinks? 

What is alcohol ? Is it a food? Does it warm the body? 
What organs are poisoned by alcohol? 
W T hat effect has tobacco ? Opium ? Coffee ? Tea ? 
What do we know of the quantity of food to be taken ? 
How does verv cold weather affect this? 



DIGESTION. 99 

What is said about the food of children? Of delicate persons? Of 
swallowing the food in a hurry? 

What are hunger and thirst? 

What are some of the principal rules to follow r in eating? 

What kind of digestion has the vegetable? 

What kind have the lowest forms of animals? 

What organs are contained in the mouth? 

What are the temporary teeth ? How many ? 

What are the permanent teeth? How many? 

How are the teeth arranged in other animals for eating insects, 
fruit, grain, or flesh ? 

What are the salivary glands ? 

What effect has the saliva upon the food ? 

What is the arrangement of the pharynx and oesophagus ? 

What are the different steps in digestion ? 

What is the diaphragm? The gastric juice? 

What are the ends of the stomach called ? 

What is the arrangement of muscles covering the stomach ? 

Describe the arrangement of the stomach in other animals, as the 
ox, the sheep, chickens, reptiles, fishes, and insects. 

What takes place in the stomach when food is taken into it ? 

What kinds of food are digested in the stomach? 

How long does food stay in the stomach to be digested? 

What becomes of these fluids when swallowed ? 

How much gastric juice is poured out in the day? 

Should liquids be taken at meal-times ? 

What are the tw T o divisions of the intestines called? 

How long is the small intestine? 

What is the arrangement of the intestines in other animals? 

What fluids are poured out into the intestine? 

How many pounds of fluids are poured out for digestion every day? 

What effect has the pancreatic juice on the food ? The bile? 

What becomes at last of all the food that has been digested ? 

What are the villi ? The chyliferous vessels? The lacteals? The 
thoracic duct ? 

W T hat are the lymphatics? What is their use? 



RESPIRATION. 



Why we Breathe. — It has now been shown in what 
way the fluids formed during digestion, and the lymph 
resulting from the wear and tear of the various parts of 
the body, pass into the blood ; but these fluids and the 
blood with which they are mixed have to be made purer 
before they are fit to nourish the body. The blood, to be 
purified, must be brought near the air which we breathe 
into our lungs. The effect of air upon the blood as it 
passes through the lungs is to change it from dark red 
to a light red or vermilion color. 

The oxygen of the air is added to the blood, and a gas 
called carbonic acid is driven off in the act of breathing. 
To show clearly to the eye that carbonic acid is given 
off from the lungs, fill a wineglass with lime-water, and 
breathe into it through a glass tube, when the carbonic acid 
of the breath will soon change the lime into chalk or car- 
bonate of lime. If we then add a little vinegar to it, the 
carbonic acid will be set free, and be seen bubbling up. 

There is also a certain amount of watery vapor dis- 
charged from the breath ; for if we breathe upon a win- 
dow-pane on a cold day it will become damp, and in the 
open air the breath will be seen as it comes from the 
mouth and nose in frosty weather. 

During respiration oxygen and carbonic acid pass 
through the delicate membrane of the blood-vessels of 
100 



RESPIRATION. 101 

the lungs. Before the blood reaches the lungs it is called 
vc'nous bfaod, because it flows through the veins and is 
of a dark bluish-red color. After it has received oxygen 
in the lungs the color is changed to a bright red or ver- 
milion, and the blood is then called arte* rial blood, be- 
cause it is carried in the arteries. 

Venous blood must be changed, because it is an im- 
pure fluid containing matters that have already served 
for the support of life in various parts of the body. 
Breathing cannot be wholly stopped for more than a 
few moments without causing death. 

Respiration includes only what takes place during the 
passing of the blood through the lungs, for when the 
purer blood leaves the lungs it is studied under the head 
of the Circulation (p. 117). 

The Chest and its Contents. — The chest is a conical 
bony cage (Fig. 2), covered on the outside and lined 
on the inside with muscles, and separated from the ab- 
do'men by a large muscle called the diaphragm (Fig. 
45), w T hich forms the floor of the chest and separates it 
from the abdomen. 

The chest is made up of a portion of the spinal col- 
umn at the back part and ribs on each side. Two large 
marble-blue organs, called the lungs, with the heart, fill 
the whole cavity of the chest (Fig. 45, C, D, E, F). 
AVhen once filled with air the lungs will always float 
in water, as may be shown with a calf's lung removed 
from the animal after death. 

The ribs are made very movable, so that they can 
rise and fall, and in this way raise and low T er the chest 



102 



ELEMENTARY PHYSIOLGY. 



during the act of breathing. Muscles pass between the 
ribs, and by their action upon them assist in respiration. 
The most important muscle is the diaphragm (Fig. 45. 
G), which is at the bottom of the chest, and moves when- 
ever w r e breathe. All the muscles of the chest and abdo- 
men take part in the act of breathing. 




Fig. 45. — Lungs, Heart, and Diaphragm in Position. 
I, pulmonary vein; 2, pulmonary artery; 3, main artery from heart; 4, 
carotid artery; 6, jugular vein; 7, windpipe; 8, larynx; 9, coronary 
A, B, C, D, heart ; E, F, lungs ; G, diaphragm. 



vein ; 5> 
artery; 



The Lungs. — In the lungs there are thousands of very 
small blood-vessels, and these are so arranged that each 
of them is completely surrounded by air. A very thin 
membrane, called the pleu'ra, lines the interior of the 



RESPIRATION 



103 



chest, and then covers the lungs and heart. It pours out 
a fluid which keeps it always moist. In very little chil- 
dren the lungs are pale red, but they get darker by age, 
and in old persons are a livid blue. When we breathe 
the air into our lungs we bring it near the warm blood 



Windpipe. 




Fig. 46. — The Lungs and Bronchial Tubes (the lung-structure on one 
side being supposed to be removed). 

that is passing through the blood-vessels in those organs, 
so that it does not chill their delicate structure. 

The air after it enters the mouth passes along the 
throat into the lar'ynx (Fig. 45), which will hereafter be 
described as the true organ of voice ; thence into the wind- 
pipe or trache'a (Figs. 45, 46), which divides into two 
large tubes or canals called the bronch'ial tubes (Fig. 46) 



104 



ELEMENTARY PHYSIOLOGY. 



One of these tubes enters each lung, and divides and sub- 
divides into a large number of very small tubes, which go 
to every part of the lung (Fig. 46), and end at last in little 

closed cavities called air- 
cells (Fig. 47). Around 
these cells are many very- 
small blood-vessels. 

The air we breathe 
does not get beyond the 
3 air-cells (Fig. 47) into 
the lung itself. These 
2 air-cells swell up after 
w T e take a full breath, and 
as long as we live they 
never get emptied of the 
air. The air-passages are 

Fig. 47.-A small Portion of the Lung H ne( J by a milCOUS mem- 
(greatly magnified). , , n . , ,, , 

brane, and a fluid called 

1, small bronchial tube; 2, termination in mucug j g e( j ^ tQ 

air-cell ; 3, tissue of the lung. x 

keep the air-tubes moist. 
The Act of Breathing. — The terms inspiration (or 
" breathing in") and expiration (or " breathing out") are 
applied to the filling and emptying of the lungs in the 
act of breathing. These acts are caused by the raising 
and lowering of the chest by muscles, especially those 
moving the ribs. When the chest contracts expiration 
occurs, and the air is driven out of the lungs through the 
mouth and nose. When we enlarge the chest by inspi- 
ration, or breathing in, we take in a large quantity of air 
to fill the lungs. The process of respiration is not under 




RESPIRATION. 



105 



the control of the will ; it goes on as long as life lasts. 
After breathing out, no matter what we are doing, 
whether talking, eating, sleeping, or reading, we have to 
breathe in, and then breathe out, and so on. 

If we take a pair of bellows, we can imagine the nozzle 
to be the windpipe, the flexible leather uniting the boards 
the diaphragm, the boards themselves the ribs, and the 
hinges the place at which the ribs are fastened to the 
spinal column. When we separate the boards of the 
bellows, it is just as if we were enlarging the chest and 
raising the ribs to fill that cavity. The air rushes into 
the nozzle as it would into the windpipe, and the bellows 
is emptied as we empty the lungs in breathing out. In 
expiration, or breathing out, the lungs empty themselves 
gradually by their own elasticity. 

We go on breathing without thinking 
or knowing that we are doing it ; and 
this is because the diaphragm is being 
raised and lowered all the time without 
calling other muscles into active play. 
When the diaphragm is lowered in the 
act of drawing in the breath, the stom- 
ach and intestines are pressed on ; in 
breathing out the diaphragm is raised, 
and the stomach and intestines return to 
their natural position. This explains 
why the abdomen seems to rise and fall 
during respiration. This is the easiest 
form of breathing ; that is, by the dia- 
phragm and muscles of the abdomen 




Fig. 48. — Gentle 
and Forced Res- 
piration (the lat- 
ter shown in the 
dotted line). 



Such easy respi- 



106 ELEMENTARY PHYSIOLOGY. 

ration is seen in those who are sleeping. In the deeper 
and more active forms of breathing, such as that occur- 
ring under excitement, a large number of other muscles 
are called into exercise, such as those of the chest. (In 
Fig. 48 we can notice the difference between the easy 
and the forced forms of respiration.) 

Number of Respirations. — As a general rule, the num- 
ber of respirations is eighteen in a minute ; that is to say, 
in each respiration the person breathes in and breathes 
out, and then a very small period of rest follows. Of 
course during exercise and motion the number of respi- 
rations is increased. In very young children the num- 
ber is much greater than in the adult. A young baby 
will breathe at least forty times a minute ; a child of five 
years of age, about twenty-five ; a grown person, about 
eighteen per minute. 

When we breathe rapidly or forcibly we call into use 
the muscles of the chest, and even those which are at- 
tached to the neck or the arm, so as to enlarge the cavity 
of the chest. Woman breathes more with the chest > even 
in gentle, easy respiration, than man. Her mode of dress 
should not be such as to press upon the walls of the chest 
or to interfere with the free motion of the ribs. 

Sounds of the Chest. — In placing the ear over the 
chest a gentle sound is heard, caused by the air passing 
into the air-cells. This sound, as well as the louder and 
rougher sound caused by the passage of air along the 
tubes, is altered by disease of those parts ; and this is 
why the physician applies his ear over the chest when 
a person has heart or lung trouble. He strikes over the 



RESPIRATION. 107 

chest with his finger, and if the sound is clear he knows 
that he is striking over a cavity filled with air ; but if 
the cells do not contain air, and have become obstructed 
from any cause, the sound w T ill be dull and obscure. 

Capacity of the Lungs. — When air enters the air-cells 
it is not wholly driven out in breathing ; a certain quan- 
tity always remains behind. It is hardly correct, there- 
fore, to say that we empty the lungs in the act of breath- 
ing. The entire air in the lungs is thoroughly renew r ed 
about once in a minute. In easy respiration the whole 
amount of the breathing capacity of the lungs is not 
called into play. The quantity of air breathed every 
minute is about ten pints. This gives an idea of the 
immense quantity breathed in the course of twenty-four 
hours. 

The Air-Cells. — The smallest bronchial tubes — capil- 
lary tubes they are called, because they are almost like 
hairs in size — are so small that from thirty to fifty of 
them measure only an inch, and it takes from seventy to 
two hundred air-cells to make an inch. An immense 
number of small, delicate blood-vessels covers the walls 
of the air-cells and the spaces between the air-cells ; and 
here the change from venous blood to arterial blood takes 
place. 

The Air we Breathe. — Pure atmospheric air is com- 
posed of two gaseous substances called nitrogen and oxy- 
gen. There is, in round terms, one part of oxygen to 
four of nitrogen. Besides the gases the air always has 
in it a little watery vapor and a very small quantity of 
carbonic acid. Oxygen alone would be too stimulating, 



108 ELEMENTARY PHYSIOLOGY. 

and respiration would be at such high pressure that death 
would soon occur. When the air is examined after it has 
been breathed out of the lungs, it is found to contain a 
much smaller amount of oxygen than when it was in- 
haled, and a much larger quantity of carbonic acid. This 
shows that oxygen has been absorbed into the lungs and 
carbonic acid given off from them. 

It will be seen hereafter that the blood contains numer- 
ous little structures called corp'uscles (signifying "little 
bodies," from a Latin word meaning "a body"), and 
these can only be seen with a microscope. These are the 
parts of the blood that are acted upon by the oxygen 
that is taken into the lungs every time w r e breathe. 

Some Ordinary Breathing Acts. — Many things we do 
in every-day life are part of the act of respiration or 
breathing. When we speak or sing or cough or sneeze 
or laugh or smell or sob or spit or yawn or snore, we are 
using our breathing organs in some way or other. 

When we sigh, it is often because the blood is not 
receiving enough pure air into the lungs, and the poor 
venous blood does not become properly changed into the 
richer arterial blood. A long sigh or series of sighs will 
supply the amount of air necessary to give to the blood 
the oxygen it needs. 

When we cough, Ave use the muscles violently that 
assist in breathing out, and at the same time we con- 
tract the muscles of the bronchial tubes, so as to drive 
out anything, such as mucus, that is there. When we 
laugh, we make the muscles used in breathing act rap- 
idly, and at the same time we use the voice and the 



RESPIRATION. 109 

muscles of expression of the face. Panting is a series 
of short, quick inspirations and expirations, and has for 
its object the rapid renewal of air in the lungs in cases 
in which the circulation of the blood is too rapid or 
where an extra supply of fresh air is required. Smell- 
ing is a series of short inspirations while the mouth is 
shut, so that the whole effect of the odor may be made 
upon the inside of the nose alone. 

How Breathing is sometimes Interfered with. — We have 
already said that the danger to life is great and immediate 
if the breathing be checked for a few moments. This may 
occur from drowning, from hanging, from anything press- 
ing on the chest too heavily, ejtc. ; but, whatever the cause 
may be, the effect is always the same : the venous blood 
is not changed into arterial blood, the proper amount of 
oxygen not being breathed in. If any one is placed 
where there is no pure air or not enough of it, or where 
there is some other kind of matter in the air, such as 
burning gas, w r hich the lungs cannot breathe, then the 
venous blood cannot be made purer and the person will 
die. Air that has once been breathed is not fit to be 
breathed again, for it is no longer pure. 

If too many persons are crowded together in a room, 
there will be so much carbonic acid breathed out from 
all their lungs and impure matter given off from their 
bodies that the room will soon be unfit to stay in, for we 
cannot breathe carbonic acid gas. They will soon begin 
to be restless and yawmy, with perhaps headache, all due 
to the bad air they are breathing. 

In a war between the English and the people of a por- 



110 ELEMENTARY PHYSIOLOGY. 

tion of India in the eighteenth century, one hundred and 
forty-six Englishmen were taken prisoners and shut up 
in a room only twenty feet square, to which but little 
light and air were admitted, and the heat was intense. 
The next morning, after only eight hours, one hundred 
and twenty-three were found dead. 

Hygiene of the Respiration. — We have seen how neces- 
sary it is that the air of rooms occupied at the same time 
by a number of persons should be properly changed and 
kept pure. Schools, concert-rooms, churches, hospitals, 
etc. should have their doors and windows and chimneys 
arranged with this view. The first and most important 
object is to give an outlet to the impure air, which, as it 
becomes warmer, will rise, and an inlet to the pure air 
from outside. Cold air is not any purer than warm. It 
is not necessary to create a strong draught of air : a gentle 
current is all that is required. One of the best modes of 
ventilating a room is the open fireplace, which makes a 
draught up the chimney, and thus carries off impure 
matters that are in the air of the room. 

Where many persons are together in a room, and no 
proper outlet is offered through windows or doors for the 
escape of impure matters from it, the place is said to be 
badly ventilated. If a long stay in an atmosphere breathed 
by healthy persons has such bad effects, how much more 
serious it becomes if we have to breathe air that is full 
of impurities from the lungs or bodies of those affected 
with disease ! Such impurities are not only unfit to be 
rebreathed, but they may give rise to serious diseases. 

The rooms occupied by both sick and well should be 



RESPIRATION. Ill 

properly ventilated by windows that will admit light 
and air during the day and keep the air pure at night. 
If fires be employed in sleeping-rooms, there must be 
sufficient outlets for the escape of the overheated air. 
Openings at the top will allow hurtful gases to escape, 
and fresh air should be admitted from without. The 
impure air at the bottom of the room should be carried 
off, by shafts into the flues or chimneys, into the current 
passing upward and outward to the external air. 

The practice of tight-lacing interferes greatly with nat- 
ural breathing. It presses upon the ribs so as to change 
the whole shape of the chest, and does not allow the ribs 
to rise and fall as they should do in the act of breathing. 
It does not allow the lungs to move freely in the chest. 
It presses upon the stomach and liver, so that they cannot 
properly attend to their duties. The healthy lungs can- 
not be thus checked in their movements, nor can the 
air be prevented from entering them in proper quantity, 
without serious consequences. The lower portion of the 
chest is naturally the largest (as seen in Figs. 2 and 45), 
and well adapted for the capacity o^ the lungs in breath- 
ing, but tight-lacing makes this the narrowest part of 
the chest. 

In breathing, the air should pass in and out through 
the nose, not through the mouth, and at night the 
mouth should be kept closed. Children and grown 
persons should stand or sit in such a way that the 
chest is not cramped, so that the lungs will act to their 
full capacity and respiration go on perfectly. 

The breathing air is sometimes poisoned by the bad 



J 12 ELEMENTARY PHYSIOLOGY. 

air or gases from sewers and drains, and from some fac- 
tories, and disease, such as typhoid fever or diphtheria, 
arises from such causes. Many persons work for a liv- 
ing in the kind of occupation that may some time or other 
injure their lungs. Those who work on steel or emery 
may breathe the very fine particles into their lungs t 
Miners may breathe a very fine dust from the mines; 
those working in paper-manufactories may inhale the 
arsenic used in making it ; or workers in white-lead 
works may breathe the fumes of the white-lead. 

Action of Alcohol upon the Respiration. — This poison 
has the effect of interfering with the change of venous 
into arterial blood. As alcohol has been show T n to irri- 
tate and excite the part into which it is introduced, its 
passage through the thin walls of the air-cells injures 
such delicate structures, producing inflammation of the 
lungs and a tendency to severe cold, pleurisy, etc. Alco- 
hol changes the shape of the red corpuscles of the blood, 
causing them to shrink up and to be wrinkled and irreg- 
ular, with notching of their edges. Habitual drinking 
of weak alcoholic liquors thins the blood, so that it 
escapes too easily from the vessels and appears near the 
surface of the body, giving the skin a swollen or bluish 
hue ; or if strong drink be habitually indulged in, the 
blood may clot and clog up the smaller vessels or the 
heart itself, and cause instant death. 

The effect of alcohol on the lungs themselves is soon 
visible. The blood-vessels are often paralyzed by this 
poison, and death results from such a condition. Even 
persons who seem capable for a while of taking alcoholic 



RESPIRATION. 113 

liquors in moderation without apparent danger may sud- 
denly be seized with disease of the lungs attended with 
cough and pain ? and rapid consumption may follow. 

Action of Tobacco on the Respiration. — Smoking of 
pipes or cigars passes the poisonous vapor directly into 
the lungs, and thence to all parts of the body. Not only 
is the nicotine of the tobacco taken in this way, but an- 
other active poison is developed in it by smoking ; and 
this is called carbonic oxide, and is much more poisonous 
than carbonic acid, producing headache, sleepiness, sick 
stomach, and irregular beating of the heart. Tobacco- 
smoking also injures the red corpuscles of the blood. 

Summary. — We may briefly sum up what we know 
of the respiration in man : The air around us loses some 
of its oxygen, but gains carbonic acid from our lungs. 
The blood changes its color from its contact with oxygen. 
The blood in the lungs loses some of its carbonic acid. 
The oxygen of the inspired air passes directly through 
the coats of the vessels of the lungs. Watery vapor is 
also discharged from the lungs. 

Respiration in Other Animals. — Eespiration in other 
animals is like that of man, so far as the passage of 
gases to and from the lungs is concerned, oxygen being 
taken in and carbonic acid given off. In the lowest forms 
of animal life, however, there are no lungs, the whole 
outside of the body being so thin as to allow the air to 
enter it, and thus to act upon the fluids contained within. 

In birds the lungs are quite small and attached to the 
chest. A large part of the chest and also of the abdo- 
men is occupied by air-cells, with large openings commu- 



114 



ELEMENTARY PHYSIOLOGY. 



nicating with the lungs (Fig. 49). In some birds there 
are cells or spaces in the bones for the air, the object 
being to make the body so light that the bird will fly 
more easily ; and it can fly and sing without having to 
take its breath all the time. Birds which fly most rap- 
idly and rise to the greatest heights — the eagle, for exam- 
ple — have a very large number of these bony cells. 



Trachea or windpipe- 



Blood-vessels of the 
lung. 



Lung 
Bronchial openings 




^—Bronchia opened. 



Bronchia opened. 



Fig. 49. — Lungs of a Bird. 



Respiration in fishes is performed by what are called 
gills, which are membranes largely supplied with blood, 
placed behind the head on each side, with movable gill- 
cover. Generally there are four gills on each side. The 
fish breathes the air that is in the water in which it swims. 
The water passes into the throat, and then through the 
openings of the gills. There is more oxygen in water 
than in the air. Some fish, however, do not get enough 
oxygen from the water, and this is why we sometimes 



RESPIRATION. 



115 



see fish rising to the surface of the water so as to get a 
larger supply. 

Reptiles do not have strong breathing powers ; some 
have lungs ; some early in life have gills ; others have . 
both lungs and gills, so that they can live both on land 
and in water. Some of them have the whole surface of 
the body arranged for the passing in and out of gases 
through the skin. The lungs of reptiles receive air that 
is swallowed rather than breathed. 

In insects, respiration is usually effected through the 






Fig. 50. — Respiration in Insects illustrated. 

A, breathing orifices of water-beetle ; B, a single opening, greatly enlarged 
C, air-tube. 

exterior of the body. The air enters through openings 
(Fig. 50) which are the ends of air-tubes and convey the 
air to all parts of the system. In all cases, however, 
there is the same kind of changing of gases in animals 
generally that has been described in the respiration of 
man. 



116 ELEMENTARY PHYSIOLOGY. 

Respiration in the Vegetable.— Vegetables under the 
influence of light absorb carbonic acid and give off 
oxygen, the carbon becoming a part of the plant itself. 
At night oxygen is absorbed and carbonic acid gotten 
rid of by them, so that plants are not safe companions 
in a sleeping-room. Portions of the plant which are 
not green, the flowers especially, absorb oxygen and give 
off carbonic acid in the light of the sun or in the shade. 



QUESTIONS. 

What is the object of breathing ? 

What gas is given to the blood in the lungs ? What gas is given 
off? How is the blood changed in the lungs? 
What organs are contained in the chest ? 
Describe the diaphragm. The lungs. 
What does the air pass through on its way to the lungs ? 
What are the air-cells and their uses? 
What do you mean by inspiration or expiration? 
What is the easiest form of respiration ? 
How many acts of respiration are there in a minute ? 
What sounds do we hear in listening to the chest ? 
How much air is breathed in a minute? 
How large are the smallest air-tubes and air-cells ? 
What is the air we breathe made up of? 
What are the acts of coughing, laughing, and smelling? 
What is the effect of crowding or of breathing impure air? 
What are the best rules for ventilating rooms ? 
What is the effect of tight-lacing ? 
What effects have occupations on the lungs? 
What effect has alcohol on the respiration ? 
What effect has tobacco on the organs of respiration ? 
Sum up what we know about the process of respiration. 
How do birds breathe ? Fishes? Eeptiles? Insects? Vegetables? 



CIRCULATION OF THE BLOOD. 



The Circulation Defined. — We must now study the 
manner in which the blood is sent to the various organs. 
The purified blood, after leaving the lungs, passes di- 



\a .«■—*», \ 




Fig. 51. — The Heart in its Natural Position in the Chest. 

a, 6, c, d, e, ribs ; 1, 2, 3, 4, 5, spaces between the ribs covered with muscles. (The 
vertical line represents the middle line of the body.) 

rectly to the left side of the heart. The heart sends the 
blood out upon its travels, to receive it once more after 

117 



118 



ELEMENTARY PHYSIOLOGY. 



it has gone its rounds and performed its duty. The 
process is called the Circulation, because the passage of 
blood all through the body and back to the heart through 
the blood-vessels is like a movement in a circle. The 




Fig. 52. — The Heart, Exterior View. 

1, right ventricle; 2, left ventricle; 3, right auricle; 4, left auricle; 5, aorta; 
6, pulmonary artery ; 7, 8, 9, large arteries branching off from aorta ; 10, vena 
cava; 11, pulmonary veins. 

discovery of the circulation was made by a physician 
named William Harvey, of London, England, early in 
the seventeenth century. 

The Heart. — The heart (Fig. 52) is a muscular organ, 
in shape somewhat like a cone, and lies in the middle 



CIRCULATION OF THE BLOOD. 



119 



and front part of the 
chest, a little to the left 
(Fig. 51), between the 
lungs (Fig. 45). It 
weighs usually about 
ten or twelve ounces, 
being, it is said, about 
the size of the fist, 
although this is an un- 
certain measurement. 
It is five inches long, 
three and a half wide, 
and two and a half 
thick. It is lined by 
a thin membrane like 
the pleura, which cov- 
ers the lungs, and is 
covered by another of 
the same kind. 

Cavities of the Heart. 
— The heart consists 
of four cavities, two 
of which receive the 
blood and two push 
it forward. The right 
side — or right heart, 
as it might be called — 
receives the dark ve- 
nous blood from the 
body, and sends it to 




Fig. 53. — The Heart and its Cavities. 
(Showing lesser and greater circulations.) 

a, right auricle; b, right ventricle, communi- 
cating through opening; c, pulmonary artery 
with branches to lungs ; d, capillaries of lesser 
circulation ; e, pulmonary veins ; /, left auri- 
cle ; g, left ventricle, communicating through 
opening ; h, aorta ; i, arteries ; k, vena cava, 
bringing blood from upper portions of body 
to right auricle ; I, m, aorta ; n, o, blood-vessels 
of stomach and intestines ; p, portal system ; 
q, portal system in liver; r, veins of liver; 
s, vena cava, bringing blood to right auricle 
from abdomen and lower portions of body; 
t, capillaries of greater circulation. 



120 



ELEMENTARY PHYSIOLOGY. 



the lungs to be changed into red arterial blood. The left 
side, or left heart, receives the blood from the lungs, and 
sends it out everywhere through the body. 

Each side has two cavities, called a.n aur'icle (meaning 
" a small ear ") and a ven'tricle (" a little stomach ") (Figs. 
52-55). The blood cannot go from the right side of the 

heart to the left with- 



out going through the 
lungs. The right 
auricle receives the 
blood, and sends it 
into the right ventri- 
cle, which forwards it 
to the lungs (Fig. 53). 
The left auricle re- 
ceives the blood from 
the lungs, and the left 
ventricle pushes it for- 
ward into large ves- 
sels called art'eries, 
which send it all 




Fig. 54. — Interior of the Heart. 



1, right ventricle ; 2, left ventricle; 3, right auri- 
cle ; 4, left auricle ; 5, opening between right through the body . 
auricle and ventricle — tricuspid valve ; 6, open- rpi -i r>, »i n ± i 
ing between left auricle and ventricle; 7, pul- 
monary artery and semilunar valves ; 8, origin heart, having more 
of the aorta with its valves; 9, 10, opening of -i -i j 

. . ^ . ' . , , work to do in send- 

vense cavae into the heart; 11, openings of pul- 
monary veins. ing the blood through 

the whole body, has much thicker muscular walls than 

the right side. The walls of the ventricles on both sides 

are thicker than those of the auricles for the same reason. 

The Greater and Lesser Circulations. — There are two 



CIRCULATION OF THE BLOOD. 



121 



kinds of circulation — one from the right side of the heart, 
through the lungs to the left side, the lesser or pulmoriic 
circulation, because it goes through the lungs (from the 
Latin word pulmo, meaning a " lung "). The other circu- 
lation is that formed by the blood passing all through the 




Fig. 55. — General View of the Heart and Great Vessels proceeding 

FROM IT. 

a, a', venae cavse ; b, right auricle ; c, right ventricle ; d, d\ pulmonary arteries ; 
e, e', pulmonary veins; /, left auricle; g, left ventricle; h, h', h", h'", main 
arteries branching off from the aorta. 

body from the left side of the heart, through the arteries 
and back by the veins, to the right side of the heart, and is 
called the greater or system* ic circulation y because it goes 
all through the system (Fig. 53). 



122 ELEMENTARY PHYSIOLOGY. 

Valves of the Heart (Fig. 54). — The opening between 
the right auricle and right ventricle is guarded by a valve 
called, from its shape, the tricuspid valve (because it has 
three cusps or points). That between the left auricle and 
left ventricle is the mi'tral valve, because it is thought to 
look like a bishop's mitre. When these valves are closed 
they prevent the blood from flowing backward. There 
are valves shaped like a half moon, called semilunar, at 
the mouth of the pulmonary artery (Figs. 54, 55) — a 
vessel which carries the blood from the right ventricle to 
the lungs — and at the origin of the aor'ta (Figs. 52, 54), 
the main artery of the body, from the left ventricle. 

Movements of the Heart. — The movements of the heart 
occur in regular succession. The two auricles contract 
and dilate at the same time, and so do the two ventricles 
soon afterward. After these movements the heart takes 
a short rest. The beat of the heart may be felt by 
placing a finger between the fifth and sixth ribs, near 
the breast-bone. When the heart contracts it alters its 
shape, and has a motion against the walls of the chest 
called its impulse. 

Movements of the heart are not under the control of 
the will. We cannot stop the heart from beating. When 
the heart contracts it sends out all the blood it contains, 
and when it dilates it fills again with that fluid. 

The beating of the heart goes on through a long series 
of years without interruption. In some animals, as the 
turtle, some serpents, and the alligator, the heart will 
continue to beat for many hours, or even days, after its 
removal from the body. 



CIRCULATION OF THE BLOOD. 123 

Sounds of the Heart. — When the ear is applied over 
the heart, two sounds are heard — one, louder than the 
other, over the lower part of the heart ; the other over 
the upper part. The words lupp, dupp, express the 
sounds heard. These sounds are connected with the 
closing of the valves, or the movement of the blood 
through the heart, or the contraction of the muscles of 
the walls. 

Course of the Circulation. — In passing through the 
heart the blood takes the following course : * The venous 
blood, when it comes back by the veins to the right side 
of the heart, enters the right auricle, which dilates and 
fills ; the auricle then contracts and fills the right ven- 
tricle. This in turn contracts and sends the blood with 
some force into the pulmonary artery, which carries it to 
the lungs to be purified. After being purified by the air 
in the lungs the arterial blood returns to the left side of 
the heart, entering the left auricle. This cavity contracts 
and sends the blood into the left ventricle, which by its 
contraction forces the blood into the arteries to be sent all 
through the body, and back by the veins to the right 
auricle, as before. The valves open freely, so as to allow 
the blood to enter, but at once close to prevent a reflow. 

The Pulse. — The series of contractions and dilatations 
is called the beat of the heart. When felt at the wrist 
or at any other part of the body where the artery is near 
the skin, as at the temple, it is called the pulse. These 
beats in a grown person average about seventy-two to the 
minute. The pulse is increased by food, exercise, or heat. 
* This should be studied in connection with Figs. 53, 54, 55. 



124 ELEMENTARY PHYSIOLOGY. 

Standing increases the number of beats, while lying down 
diminishes it. Fasting diminishes it. The greater the 
quantity of blood in the body, the greater will be the num- 
ber of beats of the heart. When we become excited the 
pulse will beat violently, giving rise to palpitation of the 
heart. When the person is affected with grief or fear ? 
the action of the heart may be so checked as to cause 
fainting, or even death. The healthy pulse may be much 
slower or faster than the seventy-two beats mentioned as 
the average. Cases have been known in which through 
a lifetime the pulse has been as low as sixty, or even less, 
to the minute. 

The pulse of a young baby is about one hundred and 
forty beats a minute, and during early childhood it is 
much more rapid than in grown persons. The pulse 
of a girl or woman is somewhat more rapid than that 
of a boy or man — about ten beats faster — although the 
heart is in size slightly smaller. 

The Heart's Work. — The heart does an immense amount 
of work during a lifetime. If we take the number of 
beats as 72 to the minute, we find that the heart beats 
more that 4000 times an hour, or more than 100,000 
times a day. A little baby's heart, beating 140 times in 
a minute, will beat in the first year of its life more than 
70,000,000 times. The only rest the heart gets is the 
momentary repose which takes place after the second 
sound of the heart. This seems to be but slight, and yet 
we find that by the end of the day the heart has had 
many hours of rest from labor. Some writers say that 
during twenty-four hours the ventricles work twelve 



CIRCULATION OF THE BLOOD. 125 

fiours and rest twelve, and the auricles work six hours 
and rest eighteen. 

The Quantity of Blood. — The ventricles send out at 
each beat or pulsation four and a half ounces of blood ; so 
that if the heart beats 72 times in a minute, there would 
be sent out in that time 324 ounces, or about 20 pounds. 
This would be about 1200 pounds every hour, or nearly 
13 tons a day, sent out by the ventricles. 

The whole quantity of blood in the body has been esti- 
mated as being in man -^ of the weight of the body ; in 
the dog, -^ ; in the cat, ^ • i n birds, -^ ; in fishes, -^-. 

It has been found by experiments that in most ani- 
mals the. blood passes all through the body in the time 
that the heart spends in making 27 beats or pulsations. 
As the heart of man beats 72 per minute, the blood would 
take only ^ of a minute in passing through the heart, 
the lungs, the arteries, the capillary vessels, and the veins, 
and returning to the heart. This w r ould be only twenty- 
two and a half seconds — surprisingly rapid, considering 
the delicate structures that the blood must pass through 
and the amount of change that takes place in it in its 
course. 

The Arteries. — The blood passes from the left ventricle 
into the aor'ta — the largest artery in the body — through 
the half-moon shaped valves called the semilunar. This 
is the beginning of the system of vessels called the ar- 
teries which carry the blood which has been purified in 
the lungs everywhere throughout the body to nourish it. 
We might compare this arrangement to the way in which 
the pipes that convey water through a city start from a 



126 



ELEMENTARY PHYSIOLOGY. 



large reservoir, and connect with smaller and smaller 
pipes to go into every street, every house, and possibly 
every room. 

The arteries (Fig. 56) are solid elastic tubes composed 
of three coats, the middle one of which is muscular and 
elastic in the larger vessels, and very muscular in the 
smaller arteries. In old times it was supposed that they 
contained air ; hence their name (from two Greek words 
meaning "to contain air "). The arte- 
ries are tough, to bear the heavy pressure 
of the blood sent into them by the force 
of the heart, and are lined by a very 
smooth membrane which allows the 
blood to pass along without anything 
to check it. 

The arteries divide until they get to 
be so small that they can only be seen 
with a microscope. Every part of the 
body is thoroughly supplied with them. 
The pulse or beat of the heart is felt 
at the wrist only because the artery is 
there near the surface. Almost all the 
other large arteries are more deeply seated, being placed 
beyond the risk of injury, protected by muscles, bones, 
etc. The pulse is felt by the physician, so that he may 
learn how strong or how regular the action of the heart 
is, and whether it is beating too often. 

Pulse- Writing. — Some one, a number of years ago, 
invented an instrument called a " pulse-writer," which 
traces on paper the course of the pulse. It has a lever 




Fig. 56.— An Ar- 
tery. 



CIRCULATION OF THE BLOOD. 127 

upon it, carried along by clockwork over a blackened 
surface, and this gives the tracing (Fig. 57). In disease 



Fig. 57. — Tracing of the Pulse at the Wrist in Health. 

this line would not be so regular. The effect of disease 
on the pulse is shown in Fig. 58, in which the tracing 




Fig. 58. — Tracing of the Pulse at the Wrist in Disease, showing a 
Double Beat. 

exhibits a double beat, which the physician knows is a 
sign of serious disease. 

The Veins. — After the blood has gone its rounds in 
the arteries it comes back to the heart by the veins. 
These are thinner vessels and not so elastic as the ar- 
teries, and they have no beat or pulsation. When an 
artery is cut the blood flows from it in jets or spurts, on 
account of the great contractility of its coats ; but if a 
vein is cut, the blood " wells out" in a stream. 

The veins are very small at their origin in the different 
organs of the body, and gradually unite to form larger 
vessels, which at last empty into the right auricle by two 
large veins, the ve'nce eav'ce, or hollow veins — one into 
the upper part of the auricle, the other into the lower 
(Figs. 53, h, s, and 54, 9, 10). This is like the plan in 



128 



ELEMENTARY PHYSIOLOGY. 




large cities of carrying off the waste water in pipes, which 
gradually get larger and larger, and at last empty the 
water into sewers or the river. 

Valves of the Veins. — The veins differ from the arteries 
in having valves (Fig. 59), which are folds 
that open to receive blood flowing in the 
direction of the heart, and close so that 
the blood cannot return in the opposite 
direction. There are no valves, however, 
in the veins of the brain and the lungs. 
The veins are generally nearer the surface 
of the body than the arteries. 

The Capillaries (from capiVlus, a hair, 
"hair-like") are very small vessels which 
are placed between the arteries and the 
veins. Through the circulation in these 
vessels the nourishment of the various or- 
gans takes place. They may be seen under 
the microscope in transparent membranes, as the web of 
a frog's foot, the wing of a bat, etc., in which we can trace 
them coming off from the arteries and finally merging 
in the veins. The more active or important an organ 
is, the more capillaries it has. 

So completely is the body supplied with these vessels 
that the slightest scratch or cut may produce bleeding. 
A grain of sand striking the eye will produce what is 
called a bloodshot eye, because there are so many of 
these little vessels in the eye. Blushing is caused by 
these vessels in the cheek filling with blood. 

Circulation in Other Animals. — The circulation in the 




Fig. 59. — Valves 
of a Vein. 



CIRCULATION OF THE BLOOD. 



129 




higher classes of animals is like that of man. The heart 
is composed of two auri- 
cles and two ventricles, 
with a double circula- 
tion, the greater and 
lesser. Animals that 
live partly under water 
have some of the ves- 
sels large and winding, 
so as to hold more blood 
while their breathing is 
suspended during their 
stay under w T ater. 

In birds the circula- 
tion is very much the 
same as in man. In 
the right ventricle, how r - 
ever, instead of a valve there is sometimes a strong mus- 
cle, which helps to force the blood to the lungs. 

In reptiles — as the tortoise (Fig. 60) — there is but one 
ventricle, and there is direct communication betw r een the 
arterial and venous blood. The blood is of course only 
partly purified. 

In fishes the heart has only one auricle and one ven- 
tricle. The blood passes from the ventricle to the gills, 
where it is changed into arterial blood, and then goes 
by a large artery like the aorta into the general circu- 
lation and back to the auricle. 

Insects, as a rule, have neither arteries nor veins. The 
fluid w T hich nourishes them diffuses itself through their tis- 

9 



Fig. 60. — Circulation of the Tortoise. 

a, a, vense cavse ; 6, right auricle ; c, g, right 
and left ventricles united in one ; d, d, pul- 
monary arteries; e, e, pulmonary veins; /, 
left auricle; n, aorta; i, large artery 
uniting at k with the aorta. 



130 



ELEMENTARY PHYSIOLOGY. 



sues. There is no heart, but a tube along the back, which 
moves like a heart. The blood is watery and without color. 
In some spiders the blood is white, but some of them 
have a kind of heart at the back, which sends out blood 
and receives it again through the lungs. In the lobster 
and other shellfish there is a heart with one ventricle — but 
no auricle — and blood-vessels, and also something like 
lungs. In the very lowest forms of animal life the blood 

or fluid which nourishes it is 
diffused through the wall of 
the digestive tube, there 
being no heart or vessels. 

The Blood itself.— The 
entire amount of blood con- 
tained in the body of a 
grown person is estimated 
at about one-fourteenth of his 
whole weight. A child weigh- 
ing thirty pounds would 
therefore have rather more than two pounds of blood 
in it. A man weighing one hundred and fifty pounds 
would have about eleven pounds of blood. The blood 
is dark red as it flows from the veins, and a bright red 
or scarlet in the arteries. It is about 100° in tempera- 
ture in man, but in some other animals it is much higher, 
as in the sheep, in which the temperature is 107°. 

The Blood-Globules. — With a microscope we find the 
blood to consist of a large number of very small red 
particles, called blood-corpuscles , blood-glob* vies, or discs, 
floating in a thin fluid called the serum. The smallest 




Fig. 61. — Human Blood-corpus 
cues (magnified). 



CIRCULATION OF THE BLOOD. 131 

drop of blood on the point of a needle contains myriads 
of them. They are of a regular and certain shape in 
the same animal, but are of different shapes in different 
animals. In the highest classes of animals, the blood- 
corpuscles are circular, while in birds and some other 
animals they are elliptical ; that is, longer in one direc- 
tion than the other. The human blood-corpuscles are 
flat discs, somewhat concave or slightly hollowed in the 
middle, with rounded edges (Fig. 61). 

To give some idea of their very small size, we may 
state that if 3200 of these red corpuscles were laid along- 
side of one another in a straight line, they would only 
occupy the space of one inch. If 12,000 of them were 
laid one on top of another, they would only occupy one 
inch in height. The serum in which they float is trans- 
parent and colorless, the redness being entirely due to 
the red corpuscles. Sometimes the corpuscles arrange 
themselves in rolls, like coin piled up together, and then 
they seem of a redder color to the eye. The size of the 
corpuscles varies in different animals, being, in man, 
32 1 oo °f an mcn m diameter ; in the elephant, 2 7*4 5 • 

White Corpuscles. — Round white corpuscles are also 
found in the blood — not so well defined as the red, although 
somewhat larger. They are much fewer in number than 
the red, and do not move along as actively in the vessels. 
In healthy blood there is about one white corpuscle to 
every four hundred or five hundred red corpuscles. The 
globules absorbed into the blood from the lymphatics and 
the chyle are developed afterward into red corpuscles. 

Number and Uses of the Red Corpuscles. — The number 



132 



ELEMENTARY PHYSIOLOGY. 




varies greatly in different animals, but in all of them they 
are to be counted by millions. It is said that five mil- 
lions of them are con- 
tained in the space oc- 
cupied by a very small 
drop of blood. One 
writer states that if the 
red corpuscles of the 
adult man were placed 
side by side on a flat sur- 

Fig. 62— Blood-crystals. f ace they would cover a 

space of about 3000 square yards. 

By chemical action beautiful crys- 
tals can be obtained from the coloring- 
matter of the blood, which under the 
microscope have the appearance pre- 
sented in Fig. 62. 

The blood-globules are really car- 
riers of oxygen, which they obtain in 
the lungs during respiration, as has 
been already shown, and they carry 
this with them to the different tissues. 
Parts which are in active exercise, 
such as the muscles and nerves, need 
this fresh supply of oxygen, and in 
the course of the wear and tear of the 
body give to the blood, by absorption 
through the lymphatic vessels, a cer- 

Fig. 63.— Coagulation tain amount of carbonic acid, which 

op the Blood. . ■ 

i, clot; 2, serum. passes along with the blood, to be 




CIRCULATION OF THE BLOOD. 133 

gotten rid of in the lungs by expiration. Life can go on 
in full health only as long as the blood-corpuscles are 
well organized and contain the proper amount of oxygen. 
Coagulation (or Clotting) of the Blood. — Blood that is 
circulating in the body consists of two portions — the red 
corpuscles and a watery portion called the liquor sanguinis 
(water or solution of the blood). When blood is drawn 
from the body a rapid change takes place in it. It be- 
comes separated in a short time into two distinct parts — 
a reddish jelly-like, trembling mass, to which the name 
dot is applied, and a yellowish liquid called the serum. 
The cause of this change is due to the separation from 
the blood of an element in it called fibrin, which is sol- 
uble in living blood and insoluble in dead blood, if we 
may so call it, or that which has been drawn from the 
blood-vessel. The fibrin leaves the liquor sanguinis, of 
which it formed a part, and draws the red corpuscles 
down with it to the bottom of the cup. The clot is there- 
fore the union of the red globules and the fibrin of the 
blood ; the serum is the thin liquid portion left behind, 
in which the other parts of the blood are dissolved 
(Fig. 63). 

Circulating Blood. Coagulated Blood. 

T • . • f Serum. Serum. 

Liquor sanguinis 1 

(Fibrin. 

Corpuscles "Clot. 

(The dotted lines show the union of the fibrin wdth the 

corpuscles to form the clot, while the serum is left alone.) 

When a blood-vessel is accidentally cut, the clots 

formed stop up the mouth of the vessel. In some ani- 



134 ELEMENTARY PHYSIOLOGY. 

mals, as birds, the formation of a clot takes place instan- 
taneously. Thus Nature seems constantly to guard the 
lives of some of the most helpless of her creatures. 
During life, while the blood is in constant circulation, 
clots rarely form, but when they do they block up the 
smaller vessels, and possibly a cavity of the heart, and 
may destroy life. 

Hygiene of the Circulation. — The healthy circulation 
of the blood is greatly assisted by exercise, by attention 
to the general health, and by other causes. Rapid ex- 
ercise, moderately employed, contracts the muscles, in- 
creases the flow of blood in the vessels, and quickens the 
action of the heart and of the circulation generally, while 
it sharpens the appetite and assists digestion. Any arti- 
cles of clothing that press too tightly on the blood- 
vessels on the surface of the body impede or arrest the 
circulation. Changes of temperature (as elsewhere shown), 
wet feet, and exposure affect the local circulation on the 
outside of the body, and the general circulation in such 
organs as the lungs or throat. 

In all the duties of life, in our meals, in our exercises, 
in our amusements, and in our work, we should never 
forget that the heart and blood-vessels have, under the 
best of circumstances, much hard work to do to sustain 
life and health. Let us do as little as we can ourselves 
to add to this labor by knowingly breaking any of the 
laws of health. 

Action of Alcohol on the Heart and the Circulation. — 
Upon the heart alcohol at first acts as a stimulant, pro- 
ducing an increase in the number and force of its beats, 



CIRCULATION OF THE BLOOD. 135 

so that the period of rest is diminished, and a greater 
amount of strain and labor thus placed upon it. If the 
number of beats be increased only five every minute, and 
this continued stimulation should become a habit, the 
heart would beat over seven thousand times a day more 
than its accustomed number. 

Although the action of the heart is thus quickened, it 
soon becomes much weakened, and requires additional 
quantities of the same stimulant to revive it. The cir- 
culation becomes irregular, being sometimes excited and 
at other times fatigued. The heart may soon beat irreg- 
ularly, or it may become dilated from over-action and the 
valves lose their power, or the membranes lining the 
cavities of the heart may become thickened and the 
blood-vessels connected with the heart diseased. The 
heart may suddenly fail to do its work or the vessels 
become ruptured, and the blood flowing continuously 
through the heart will be thrown back upon other or- 
gans, as the brain or lungs, and produce violent death 
at any moment. 

Alcohol, as we have already seen, passes at once into 
the blood-vessels of the stomach and goes directly to the 
liver. Some of it may get into the bowel and be absorbed 
into the lacteal vessels, and pass into the blood in that 
way. Whatever route it takes, it gets rapidly to the 
heart ; but when it goes to the liver directly it soon gets 
into the main stream of blood. This is why a drink of 
brandy or gin soon goes to the head, as it is called, and 
acts upon the brain. Every part of the body feels the 
effect of the poison. The brain, the liver, the lungs, 



136 ELEMENTARY PHYSIOLOGY. 

and the heart, all receive it as it reaches them mixed 
with the blood as it goes to and through every organ. 

The flow of blood through the vessels is regulated by 
a central system of nerves not under the control of the 
w T ill.' The use of alcohol as a drink paralyzes these 
nerve-centres, and also the little nerves w T hich control 
the action of the small vessels, so that the man who 
drinks alcohol as a habit soon gets redness of the face 
and of the nose, because the little vessels in these parts 
of the body get too full of blood and remain so. The 
eye itself and the lids become inflamed and red, and con- 
tinue so. The blood-vessels in other parts become diseased 
and lose their elasticity, and of course this gives the heart 
much more to do. 

The nerve-centres that regulate the motions of the heart 
also become paralyzed, and the blood is not driven from 
its cavities regularly and quietly, as in health, and the 
drinker dies from a heart overworked by alcohol. 

Action of Tobacco on the Circulation. — Tobacco makes 
the blood too fluid and causes palpitation of the heart. 
Its continued use injures the red corpuscles of the blood, 
and greatly disturbs the action of the heart and blood- 
vessels. It has been shown recently that while the pulse 
is 72.9 among non-smokers, the average pulse of those 
addicted to the use of tobacco is 89.9 — an increase of 
about seventeen pulsations of the heart every minute. 
This is to say, that to every thousand pulsations in one 
who does not smoke there would be one thousand two 
hundred and thirty-three pulsations in him who does 
smoke. The effect of such increased action of the heart 



CIRCULATION OF THE BLOOD. 137 

must be very injurious, giving it increased labor, and in- 
creasing the number of beats of the heart about twenty- 
four thousand every day. 

The Effect of Narcotics. — Opium, Indian hemp, chloral, 
and other articles that are resorted to so blindly by many 
persons under the mistaken idea that they derive pleasure 
from their use, all affect the heart or the circulation 
through their influence on the nervous system. They 
should be avoided as poisons, which should not be used 
except under the advice of a physician, who will pre- 
scribe them for their qualities as medicines. Their effects 
will be studied more fully when we come to consider the 
Physiology of the Nervous System. 

Mortality from Alcohol. — A recent writer states that no 
less than twenty diseases are acquired by the use of 
alcoholic liquors. Premature decay and old age might 
be added to the list. The deaths from alcohol are very 
many, as the diseases caused by its use attack those whose 
constitutions are already weakened by drink and are often 
beyond the reach of medical aid. Another writer states' 
that in Great Britain and Ireland at least a hundred deaths 
occur every week from alcoholic excitement, and a thou- 
sand deaths every week from the diseases which follow 
from the use of alcohol. 

Materials Separated from the Blood. — While the blood 
is going the round of the circulation there are little bodies 
called cells which are busy taking from the blood such ma- 
terials as are of no further use in the body. This is the way 
that the tears and the perspiration are formed, and through 
them we get rid of some matters that are not nourishing. 



138 



ELEMENTARY PHYSIOLOGY. 



The pancreatic juice and the bile and the saliva are all 
specimens of secretions, so called ; that is, of fluids sep- 
arated from the blood by the action of cells, for secretion 
means nothing more than separation. The bile, for in- 
stance, is secreted by the liver. 

Secreting Structures. — The simplest arrangement for 
secretion is like filtering from a very small blood-vessel 



d e / 




Fig. 64. — Arrangement of Secreting Structures. 

A, a, cells ; 5, membrane; c capillary blood-vessels; B, simple glands, showing 
their different kinds of secreting apparatus ; d, straight tube ; e, sac ; /, coil of 
tubes; C, compound tubular gland; D, gland arranged like bunch of grapes; 
E, other shapes of glands. The dotted lines represent the layer of cells through 
which secretion is effected. 

through a membrane (Fig. 64, 6, c). In more compli- 
cated organs, like the liver, the action of cells is also 
required, so that they can choose the proper materials to 
make the bile (Fig. 64, a). To get plenty of surface for 
secretion, the membrane is turned in as shown in Fig. 64. 
A single inch of skin in this way becomes lengthened into 
many yards. Some of the glands are made up of tubes 
(Fig. 64), some are in shape like a bunch of grapes (Fig. 
22), while others are mere sacs. 

Glands. — The organ or body whose duty it is to sepa- 
rate materials from the blood is called a gland. We have 



CIRCULATION OF THE BLOOD. 139 

glands in the skin (Fig. 80), and the liver and pancreas 
are also glands. They have a canal leading from them 
to carry off the fluid which they have been forming. The 
bile is poured out by a canal into the intestine ; the per- 
spiration is poured over the surface of the skin through 
thousands of little tubes leading from the sweat-glands. 

In the lower back part of the abdomen are two of the 
most important glands of the body — the kidneys — one on 
each side of the spinal column. A large amount of blood 
is sent to them, and from this blood useless solid and liquid 
materials are separated, to form a fluid which afterward 
passes, drop by drop, into a sac called the bladder. 

QUESTIONS. 

What do we mean by the Circulation ? 

State size, position, etc. of heart. What are its cavities? 

What are the two circulations? The valves and their uses? 

What are the movements of the heart ? The sounds of the heart ? 

What is the course of the blood after leaving the heart? 

What is the pulse ? In childhood ? In grown persons ? 

How much blood is there in the body ? 

What are arteries ? Veins? Capillaries? What is pulse-writing? 

What is there in the veins to prevent the blood from flowing back ? 

How do exercise, etc. promote the circulation ? 

What is the action of alcohol on the heart? On circulation? 

W r hat effect have tobacco and narcotics ? 

How is the circulation carried on in other animals? 

Of what parts is blood composed ? 

What do we know of the blood-corpuscles ? Their uses ? The white ? 

What is coagulation due to ? 

What materials are secreted from the blood ? By what agency ? 

What is meant by a secretion ? Give examples. How effected ? 

What is a gland? How is the fluid from glands carried off? 

What is the simplest arrangement for secretion ? 



ANIMAL HEAT. 



Temperature of Animals. — The temperature of the body 
of man and other animals is known as animal heat. Each 
animal has a temperature which does not usually vary. 
Such animals are known as warm-blooded. Those ani- 
mals whose temperature is not constant, and not much 
above that of the air or the water in which they live, are 
called cold-blooded. Reptiles and fishes are cold-blooded. 

A great deal of oxygen is taken into the lungs in 
breathing, and a part of it unites, all through the body, 
with some of the chemical parts of the food, such as 
carbon and hydrogen. This union gives rise to heat. 
Every chemical change which occurs in the body results 
in the production of heat. The more active the respira- 
tion and the more nourishing the food, the greater the 
amount of heat. 

Where the respiration is slow and inactive, as in rep- 
tiles, the animal heat is not high. Increased exercise 
raises the temperature. In the Arctic regions more food, 
especially of an oily and fatty kind, is taken than by 
those living in milder climates. The animal heat is re- 
duced during starvation, and in such a condition freezing 
to death takes place rapidly. 

140 



ANIMAL HEAT. 141 

Temperature of Different Organs. — AVhen a ther- 
mometer is placed in the armpit or beneath the tongue, 
it registers in health from 98° to 99° (Fahrenheit), and 
the temperature of the body generally is stated to be 98 J°. 
It usually varies but a degree or two in health. In young 
children the temperature is about two degrees higher than 
in grown persons. In some diseases, such as typhoid 
fever, there is an increase of the heat of the body, while 
in cholera it may fall many degrees. 

The temperature of some of the organs, as the lungs 
and the muscles, is rather higher than that of the surface 
of the body. The blood is hotter on the right side of the 
heart than on the left, and cooler when it leaves the heart 
after passing through the lungs. It is cooler in the veins 
near the surface of the body than in the arteries, but in 
interior organs the blood coming from them by the veins 
is warmer than that going to them by the arteries. 

Friction, muscular movement, etc. give rise to addi- 
tional heat. The greatest amount of heat is produced in 
the liver and by the muscles, and it is found that the 
blood is warmer after coming from a muscle than it was 
in going to it, thus showing the effect of motion in pro- 
ducing heat. 

Hygiene of Animal Heat. — Man, having an even tem- 
perature in health, and being able to regulate his food 
and exercise, as well as to protect himself against intense 
heat or cold by proper clothing, can bear great heat or 
cold better than any other animal. ~No matter what the 
climate or season, the heat of the human body remains 
very nearly the same. 



142 ELEMENTARY PHYSIOLOGY. 

The heat of the body is not much affected, even in 
those who have to work in very high temperatures, such 
as those of iron-works, furnaces, etc. The effect is 
warded off by the increased amount of perspiration pro- 
duced by such exposure. During such evaporation heat 
is abstracted, and the part becomes really cooler; the 
more rapid the evaporation the more decided the sensa- 
tion of cold. 

In warming the rooms we occupy in winter we endeav- 
or to prevent the heat of the body from being too rap- 
idly lowered. The heat of the body is always higher 
than that of any artificial heat we obtain or could bear 
in our residences. In cold seasons there is but a small 
amount of perspiration poured out, so that evapora- 
tion can produce but little coldness of the surface, and 
there will be only a slight reduction of the heat of the 
body. 

The chemical changes causing animal heat take place 
through the agency of the capillary blood-vessels which 
are found everywhere through the body. 

Clothing is necessary to prevent too rapid loss of heat, 
either from contact of the surface with cold air or from 
the evaporation of the perspiration ; the material used 
for the purpose depends on the fact of its being a non- 
conductor of heat. Porous materials are usually em- 
ployed for this purpose, as the pores or openings are 
filled with air and their conducting power for heat is 
low. Wool, silk, cotton, and linen are the articles gen- 
erally used. 

The material of which the clotiiing is made is import- 



ANIMAL HEAT. 143 

ant for the health. Woollen clothing is employed be- 
cause, being a poor conductor of heat, it does not allow 
the natural warmth of the body to escape through it, and 
it absorbs the perspiration without becoming moistened 
by it. For these reasons flannel is worn, or should be 
worn, next to the skin at all periods of the year ; even, to 
a slight degree, during the summer season. In milder 
climates cotton may be worn ; it readily absorbs moisture. 
Linen is a cool material for wear in summer, as it is a 
good conductor of heat and rapidly carries off the warmth 
of the surface. Silk is a good non-conductor of heat. 

When the skin is rapidly chilled by exposure of any 
kind, what is popularly known as " taking cold " results 
— the blood at the surface temporarily receiving a shock 
by which the blood is sent in unusual quantity to the 
interior of the body, some part of which may become 
congested and inflamed, producing sore throat or inflam- 
mation of the lungs. Warni applications and the use 
of such internal medicines, under proper advice, as will 
stimulate the secretion of the skin and the blood to more 
active circulation toward the surface of the body, will fre- 
quently relieve the " cold/' 

Action of Alcohol on the Temperature. — If a delicate 
thermometer be placed under the tongue of a person who 
has taken a quantity of alcoholic drink, it will be found 
that, though there may at first be a slight increase in the 
temperature, there will soon be a reduction in the natural 
heat of two or three degrees, lasting for several hours. 
At first, after taking alcohol, there is a slight feeling of 
warmth, but there is no real increase of heat. If the 



144 ELEMENTARY PHYSIOLOGY. 

skin is warmer, it is because the natural heat has been 
taken from organs inside the body. This heat of the 
skin is soon lost, and the general heat of the body is 
lowered, because so much blood is carried to the surface. 
Alcohol lessens the power to bear extreme heat or cold ; 
those who live in the coldest regions do not use it. 

Effect of Tobacco on the Temperature. — In some ob- 
servations recently made in France it was found that the 
mean temperature of the body for the twenty-four hours 
in non-smokers of average constitutions was about 98° 
Fahr., while in those addicted to the use of tobacco the 
mean temperature was 98.6° Fahr. In those of weak 
constitutions the temperature rose to a much higher de- 
gree. Tobacco, therefore, may be said to raise the tem- 
perature of the body nearly one degree. 



QUESTIONS. 

What is meant by animal heat ? 

What are warm-blooded and cold-blooded animals? 

What effect has oxygen in producing animal heat ? 

By what kind of action is the heat of the body produced? 

What effect have food, respiration, and exercise in producing heat? 

What is the temperature of the body ? Of young children ? 

Is the external or internal temperature the highest ? 

On what side of the heart is the blood the hotter? 

In what organs is the greatest amount of heat produced ? 

Why is man able to tolerate excessive heat or cold ? 

What effect has evaporation on the heat of the body ? Clothing? 

What blood-vessels are concerned with animal heat ? 

What is "taking cold"? 

What effect has alcohol on the animal heat? Tobacco? 



THE NERVOUS SYSTEM. 



Peculiar to Animals Alone. — The vegetable has not any 
nervous system. By it man feels and thinks and moves 
at will. By it he lives, although he may be asleep, 
and the nutrition of his body goes on whether waking 
or sleeping. 

Divisions of the Nervous System. — One of the great 
divisions of the nervous system consists of the brain and 
spinal cord as centres, and is therefore called the cere'bro- 
spi'nal system (from cerebrum, "brain"), (Figs. 67, 68). 
Slender white cords, called nerves, pass from them, which 
divide and subdivide until they get to be very small in- 
deed, and every part of the body is supplied with them. 
There is not a point of the skin which does not, when 
cut or pricked with a pin, show by the pain that it is 
fully supplied with these little nerves. 

Another part of the nervous system is called the syra- 
pathet'ic system, because it brings all parts of the body 
into direct sympathy with one another (Fig. 74). Its 
nerves communicate with the nerves of the other system 
to make the chain of sympathy complete. If it were not 
for such a nervous system, each organ would be acting by 
itself, and perfect health would be impossible. 

Nervous Matter. — This is a soft substance, almost fluid 
at birth. Under a microscope it is seen to be made up of 
a white and a gray matter. The white substance is made 

10 145 




Fig. 65. — General View of the Nervous System. 

a, cerebrum, or brain proper ; b, cerebellum, or little brain ; c, spinal cord ; d, 
nerve of face; e,f, g, h, nerves of arm; ?', nerves between ribs; k, nerves of 
lower part of back ; I, nerves in region of hip ; ??i, n, o, p, nerves of the leg. 



THE NERVOUS SYSTEM. 



147 



up of delicate nerve-fibres about the Q ^ Q0 of an inch in 
diameter. The gray or ash-colored matter is made up of 
nerve-cells of various sizes, rounded, with a central spot 
on each (Fig. 66). White fibres are largely found in the 
long cords, called nerves, which pass to and from the 
various parts of the body. The outside of the brain is 
made up of gray matter ; the inside, of white matter. 
The gray matter gives origin to nervous power; the 
white carries it. 




Fig. 66. — Various Forms of Nerve-cells. 

The Cerebro-Spinal System. — The central parts of the 
cerebro-spinal system (Figs. 67) are the brain and the 
spinal cord, both of which are soft masses of white and 
gray matter. The part contained in the skull is the 
brain; that in the spine is the spinal cord or spinal 
marrow. 

All these parts (Fig. 67) are protected from injury by 
bones and by membranes covering them. For this rea- 
son a blow or a fall on the head does not injure the brain 
as much as it would if the brain had been nearer the sur- 
face. The brain and spinal cord are both covered with 



148 



ELEMENTARY PHYSIOLOGY. 



three coats, one within 
the other, the outer coat 
brum, being thick and strong, 
and dipping down be- 
tween folds of the brain 
to protect it from being 
pressed upon. One of 
these coats is as thin as 
a spider's web. 

The Brain (Figs. 67, 
68, 69).— This organ, 
placed in the skull, 
is divided into three 
parts — the brain proper, 
or cere'brum, the large 
round mass which fills 
the greater part of the 
skull ; the little brain, 
or cerebellum, a smaller 
portion at the lower and 
back part of the skull ; 
and a still smaller part, 
the meduVla oblongata, 
which, translated into 
English, means the spi- 
nal cord prolonged (into 
the skull). There is a 

Fig. 67. — The Brain and Spinal Cord. ]^pg , e ODenillff ill the 

under and back part of the skull for the very purpose 
of allowing it to pass through. 




Spinal 
cord. 



THE NERVOUS SYSTEM. 



149 



Seven-eighths of the space in the skull occupied by the 
whole brain belongs to the cerebrum, or brain proper. 
This part of the brain is the seat of the mind or intelli- 
gence of the animal. 



Convolutions of cerebrum. 




Cerebellum. 



Medulla oblongata. 



Fig. 68. — Interior of the Brain (showing, by section through it, its 
various parts). 

Weight and Size of the Brain. — The average weight 
of the brain of man is a little over three pounds. The 
brain of woman is generally from four to six ounces 
lighter. The brain of an idiot seldom weighs more than 
23 ounces. Some human brains have been found after 
death to weigh between 60 and 70 ounces. 

The brain proper of man is greater in proportion to 
the weight of the body than that of any other animal. 
The brain of the elephant weighs only 120 to 150 or 160 
ounces, and of the whale about 80 ounces. This is a 



150 



ELEMENTARY PHYSIOLOGY. 



much smaller amount of brain, in comparison with the 
size of the animal, than that of man. The brain of the 
elephant is only the -g-J-g- th part of the weight of his whole 
body, while in man it is about the y^th. 

The Caucasian race, including the European and Ameri- 




Fig. 69. — Exterior View of the Brain. 
1, 1, right and left hemispheres of brain ; 2, 2, crack or fissure dividing the brain 

can, has the brain more fully developed than any other. As 
the front part of the brain is the seat of intellect, the 
prominence of the forehead has been considered a sign 
of intelligence. 

The Brain Proper. — The cerebrum, or brain proper 
(Fig. 68), is made up of thick, worm-like folds called 
convolutions, having deep cracks between them (Fig. 69 ? 



THE NERVOUS SYSTEM. 151 

2, 2). The brain is made up chiefly of fat and phos- 
phorus. The principal crack or fissure of the brain divides 
it into two parts, called hemispheres (Fig. 69, 1, 1). 

The outer part of each hemisphere is made up of gray 
or ash-colored matter, but the interior is almost entirely 
white matter. At the base of the brain are bodies, called 
gang'lia, made up of gray matter, through which the 
fibres pass from below upward to the brain. 

In the brain is quite a variety of cavities or spaces, 
with arches and delicate veils and odd-looking halls and 
passage-ways, of whose uses we know little or nothing. 

Cerebellum. — The little brain, or cerebellum (Figs. 67, 
68), is not in convolutions, but in layers like the leaves 
of a book. When cut into, it has the appearance of a 
tree, and is therefore called ar'bor vi'tce, or " tree of life." 

Spinal Cord (Fig. 67). — The cord, or spinal marrow, 
is a combination of cords of nervous matter, separated 
by fissures running their whole length, and covered by a 
membrane common to all. Before passing into the skull 
the fibres from the right and left sides of the cord pass 
across and into one another, and then go up into the 
cerebrum or brain proper, in which they spread out in 
all directions. 

The Nerves (Fig. 70). — These are continuous threads 
of nervous tissue which are sent to all parts of the body. 
They are made up of collections of little nervous threads 
or filaments bundled together. Each filament is com- 
posed of a fine gray thread, surrounded by a soft white 
substance, enclosed in a thin covering. They are very 
numerous on the skin. They convey impressions back- 



152 



ELEMENTARY PHYSIOLOGY. 



ward and forward , to and from the surface of the body 
or from organ to organ within the body. They are the 

telegraphic svires through which 
the will and the mind, and even 
life itself, make themselves 
known. 

After a nerve nears the sur- 
face, where, by motion of the 
limbs or by pressure, it might 
suffer, it becomes covered with 
a strong white covering, called 
the nerve-sheath, which binds 
together the different filaments. 
In the course of some nerves, 
as the great sympathetic nerve, 
there are enlargements or knots 
called ganglions. 

The nerves do not communi- 
cate with one another, as the arteries and veins do, by 

open vessels. In Fig. 71 is 
shown a representation of tub- 
ular nerve-fibres from different 
parts. They are very distinct 
from the nerve-cells already 
alluded to, and assist in carry- 
ing nervous influence. 

The Nerves in Pairs. — The 
nerves come off from the brain 
and spinal cord in pairs — that 
is, one from each side of the axis right and left. Those 




Fig. 70. — A Nerve and its 
Divisions. 




Nerve-fibres. 



a, b, c, d, nerve-tubes of different 
sizes; e, nerve-tube from sym- 
pathetic. 



THE NERVOUS SYSTEM. 



153 



which come directly from the brain and spinal cord 
number altogether forty-three pairs. There are twelve 
pairs of cranial nerves and thirty-one pairs of spinal 




Fig. 72. — Nerves on the Surface of the Face and Neck. 
(The guiding lines indicate the most important nerves and their branches.) 

nerves. Those coming from the brain pass out to various 
organs through openings in the skull ; the spinal nerves 
through openings in the spinal column. 

Cranial Nerves. — The cranial nerves supply the organs 



154 



ELEMENTAKY PHYSIOLOGY. 



of sight and smell and hearing, the face (Fig. 72), the 
mouth, and the tongue and throat ; and some of them go 

to the heart and lungs and 
stomach. The fifth pair of 
nerves is sent to the face, the 
eye, the nose, the mouth, etc., 
and gives feeling to those parts 
(Fig. 72). Some persons when 
puzzled scratch their heads or 
rub their foreheads, and in 
doing these acts they stimulate 
branches of the fifth pair ; as 
other persons do who, when 
thinking, strike their fingers 
against their noses. Others 
do the same by taking snuff. 
Some of the cranial nerves 
are connected with the mo- 
tions of the face ; some are 
merely nerves of special 
senses, like hearing and sight, 
and would cause no feeling 
of pain if cut or injured. 

Spinal Nerves. — These, as 
they issue from each side of 




Fig. 73. — Origins of the Spinal 
Nerves from the Spinal Cord. 



A, A, A, anterior roots which unite 
afterward to form the fibres of the 
root ; P, P, P, posterior roots ; C, D, 
filaments passing between the pos- 
terior roots ; g, g, g, ganglions of the spinal cord, have two 

posterior roots : M, M, nerves . , . , . . p . -i 

f , , . . . . roots, which iom to iorm tne 

formed by union of two roots. J J 

(The size of the roots is larger than nerve before it passes through 

the spinal column. The sub- 
stance of the spinal cord consists of gray and white mat- 



THE NERVOUS SYSTEM. 155 

ter, but differently arranged from that in the brain, the 
white substance being on the outside, the gray on the in- 
side. Three coats cover the cord, similar to those of the 
brain. The fibres which make up the larger root of each 
spinal nerve are nerves of sensation, while those which 
form the anterior or lesser root are nerves of motion. 
On the posterior root is a small ganglion (Fig. 73). 

The nerves w T hich are sent out from the spinal mar- 
row convey feeling and motion to the most distant points. 

The Great Sympathetic Nerve (Fig. 74). — This nerve 
consists of a series of small nervous bodies or ganglia 
connected by nervous cords and threads, and communi- 
cating with the other great nervous systems. It spreads 
itself through the most important parts of the body, 
especially the chest and abdomen, and on each side of 
the middle line in front of the spinal column. It has a 
place also in the brain, from w T hich muscles of the eye and 
ear and other organs are supplied. It has much to do with 
several of the processes that maintain life, as digestion, 
respiration, circulation, etc., but has nothing to do with the 
great acts of the mind or with the motion of the person at 
will. These are controlled by the cerebro-spinal system. 

The small bodies, or ganglia, of the sympathetic nerves 
(Fig. 74) start out nerve-power and send it along the 
nervous wires to the various organs. Branches are sup- 
plied to the muscular coats of the blood-vessels, which 
regulate the quantity of blood they may contain. Blush- 
ing and paleness of the face are examples of this influence. 

Functions of Nervous System. — When an impression 
is made on any part — as by a blow or by excessive 




Fig. 74. — The Great Sympathetic Nerve. 



1, 2, 3, ganglia in the neck; 4, spinal ganglia; 5, 6, branches going to heart; 7 
nerves about diaphragm; 8, nerve to digestive organs; 9, semilunar ganglion; 
10, 11, 12, nerves to abdomen ; 13, small nerves going with arteries to brain. 
Dotted lines show position of a, heart, and b, diaphragm. 



THE NERVOUS SYSTEM. 157 

heat or cold — the very small nerves of the skin carry 
it inward along other nerves to the brain. These impres- 
sions are the sensations with which we are so familiar. 
The brain is the seat of the will ; and the nerves going 
back to the skin receive another impression from the 
brain, and send or carry it to a particular muscle or 
organ, which they thus call into motion or action. 

We thus learn that there are two sets of nerves — one 
set called sens' ory nerves, or nerves of sensation ; the other 
set mo'tor nerves, or nerves of motion. 

If the hand be accidentally brought into contact with 
a hot substance, a sensation of pain is sent to the brain 
by the nerves of sensation, and the hand is at once re- 
moved, by what seems a message sent through the nerves 
of motion to the proper muscles. 

When w r e are asleep the gray part of the spinal cord 
takes notice of impressions from without. The rest of 
the spinal cord and the brain are connected with this gray 
matter of the cord. The 
impression is made on 
the skin first, and carried 
thence to the spinal cord, 
which calls the proper 
muscles at once into ac- 
tion. This is called re- FlG ' 75 - s ™ PLE Reflex Acti ™- 

1, the skin ; a, nerve to spinal cord ; 6, spinal 
jieX ClCllOn (-Tig. /5j. cord; c, nerve to muscles. (The nervous 

When We throw U"n influence travels in the direction indi- 

* cated by the arrows.) 

the arm as a shield from 

a blow, we do it by this reflex action. If we lay hold of 

a substance that is too hot to hold, we drop it through 




158 ELEMENTAKY PHYSIOLOGY. 

this reflex action. During sleep the mouth will receive 
and the throat sw r allow water when placed to the lips ; 
the body will turn in bed during sleep by the same kind 
of reflex action. 

Functions of the Medulla Oblongata. — This is the link 
between the brain and the spinal cord. It chiefly takes 
charge of the breathing or respiration and swallowing 
or deglutition. Of course all impressions going to or 
from the brain, from or to the spinal cord, pass along it 
(Fig. 68). 

Functions of the Cerebellum. — This part of the brain 
(Fig. 68) regulates and keeps in order the motions of 
man and animals. In experiments on animals, when 
this part was cut, the animal could not move, fly, walk, 
or even stand. 

In some experiments on pigeons — which seemed im- 
portant at first to establish the fact, but which can hardly 
be considered necessary now merely to gratify idle curios- 
ity — it was found that if the cerebrum, or brain proper, 
was taken away the animal would remain firm on its 
feet, while a pigeon from which the cerebellum was only 
partially removed was as unsteady as if it was drunk. 
The cerebellum does not originate movements, but it 
regulates and gives precision to them. 

Functions of the Cerebrum, or Brain Proper. — The 
cerebrum, or brain proper, is the great organ of thought, 
sensation, and the mind, and of voluntary motion. The 
brain of man is in size and development far superior to 
that of all other animals. It has been thought that the 
two hemispheres of the brain may act — that is, think — 



THE NERVOUS SYSTEM. 159 

separately as well as together. Our minds certainly wan- 
der off to a hundred other fancies while w r e seem to be 
interested in only one subject. 

Sleep. — The active exercise of the brain is of course 
checked during sleep ; respiration, digestion, and circula- 
tion go on, but not so actively as when we are awake. 
The amount of necessary sleep depends on the age and 
habits. The very young require a great deal of sleep, 
because all their organs are so active that they must have 
rest ; old people, because they are feeble. There seems to 
be less blood in the vessels of the brain during sleep. 
Eight hours are usually required by grow r n persons, and 
more than this by children. 

When the brain becomes active during sleep dreaming 
results, but this may be due to disturbance of the diges- 
tive organs, as after a full meal. 

The Nervous System of Animals. — Animals next to 
man in the scale have the same organs for a nervous sys- 
tem that he possesses. Those lower in the scale have the 
hemispheres of the brain less and less developed. Other 
portions of the brain are less perfect, and some parts en- 
tirely absent. In the low r est forms of animal life the 
nervous system seems to be absent. 

In insects nerves are found in the organs of digestion 
and circulation like the sympathetic system in man. In 
some of them ganglions are arranged like a chain, from 
which nerves are given off (Fig. 76). 

In animals which have a spinal column the nervous 
system is along the back part of the body. They have 
a brain and spinal cord. As we ascend in the scale the 



160 



ELEMENTARY PHYSIOLOGY. 



hemispheres become larger and the convolutions deeper 
and more developed. 

Hygiene of the Nervous System. — The nervous system 

must be cared for in every 
possible way, as by health- 
ful exercise, by rest, and by 
sleep. Sound and regular 
sleep, especially at night and 
after fatigue, will do much 
to revive it. If we will 
take care of the health of 
all the other organs, we will 
have the nervous system 
healthy also. The brain and 
nervous system should not 
be overworked. Steady men- 
tal work does the brain good 
if a person does not neglect 
the other organs of the body. 
Mental worry and anxiety in 
study or in the affairs of the 
world break down the ner- 
vous system and the general health. Regular study at 
school or at home, regular habits and regular meals, reg- 
ular exercise and regular sleep, will keep the brain and 
nervous system in good health. 

Action of Alcohol upon the Nervous System. — The effect 
upon the brain of small quantities of alcohol taken occa- 
sionally is to increase the amount of blood going to that 
organ. This is still more marked if the quantity be 




Fig. 76. — Nervous System of 
Insects. 

A, grasshopper; B, stag beetle. 



THE NERVOUS SYSTEM. 161 

increased, and alcohol be taken as a habit. The condition 
resulting from abuse of intoxicating liquors is called 
al'coholism. The coats of the blood-vessels become 
weak in such persons, and they give way and produce 
apoplexy ; that is to say, the blood passes from the blood- 
vessels into or upon the brain-substance. Besides this, 
the brain-substance is hardened and wasted away, and 
water is found in the cavities of the brain. 

The person so affected by alcoholic drinks soon gets 
his mind clouded and confused with delusions of various 
kinds ; it does not have rest ; there is loss of sleep ; he 
cannot think or reason properly ; his muscles are not 
steady; and he has intense desire for drink. 

Under such a condition of his mind the moral powers 
become affected, and crime and poverty soon follow. 
When once formed, the habit of drinking controls him ; 
he becomes in every sense a moral, mental, and physical 
wreck, from which death is often a relief to himself and 
his friends. 

It is fully proven that crime keeps pace with drunken- 
ness, and wicked deeds of every description occur much 
more frequently in those places in which alcoholic liquors 
are indulged in to excess. Drink is the exciting cause 
of crime in a vast number of cases. 

In its effects upon the brain and nervous system gen- 
erally alcohol belongs to the class of narcotics (from a 
Greek word meaning " stupor "). Its first effects are 
stimulant, and seem to increase the activity of the mus- 
cles and to excite increased warmth and activity of the 
mind ; but these effects are transient and deceptive. If 
11 



162 ELEMENTARY PHYSIOLOGY. 

the habit be continued, self-control is lost and the man 
becomes thoroughly poisoned. Sounds are heard that have 
no reality, objects are seen which have no existence, and 
a condition known as delirium tremens or ma'nia-a-po'tu 
("mania from drink ") results. Sometimes paralysis or 
loss of power of both mind and body occurs, from the 
action of the poison upon the nervous matter and upon 
the membranes covering the brain and spinal cord ; and 
death soon follows. 

The children of parents who have been alcohol-drink- 
ers are more likely to get nervous diseases than other 
children. The sins of the fathers are thus often visited 
upon the children. 

Action of Opium upon the Nervous System. — Opium 
is a poison of the narcotic class, which, when properly 
given, under medical advice, is capable of acting as a 
valuable remedy in relieving pain, producing sleep, etc. ; 
but when it is used for self-indulgence the habit will 
sooner or later wreck the unhappy individual who in- 
dulges in it. Opium is the thickened juice of the poppy. 
Morphia is its active principle, and laudanum, paregoric, 
and Dover's powder, and similar preparations owe their 
virtue for relieving pain and causing sleep to the opium 
which is in each. Opium is sometimes given to very 
young children to produce sleep, but it is a dangerous 
poison, and death will occur sometimes from the giving 
of even the smallest doses — a drop of laudanum, for in- 
stance. " Drops," " soothing syrups," etc., given in this 
way, may kill the child. 

The "opium-habit," "morphia-habit," etc., as it is 



THE NERVOUS SYSTEM. 163 

called, shows its effect on the nervous system by the 
dulling and weakening of the powers of the intellect. 
After taking opium or other narcotics to produce sleep, 
the individual awakens to a disturbed and unsettled feel- 
ing of unrest of a most distressing kind. The same re- 
sults follow the use of opium, whether it be smoked or 
eaten, except that a larger quantity will be taken in the 
latter way. Paralysis frequently occurs as a result of its 
use. 

Action of Chloral and Other Narcotics. — Chloral is 
made from alcohol by a peculiar chemical action. Like 
opium, it may be abused by self-indulgence until the 
chloral-habit becomes as firmly settled as the opium- 
habit. It soon impairs the digestion and circulation, dis- 
turbs the action of the heart and nervous system, and 
before long sleep cannot be procured without it. 

Indian hemp is sometimes taken to intoxicate, on ac- 
count of the drowsiness and dreaminess produced by it ; 
but the effect of all such articles, taken as a habit, is to 
excite and cloud the intellect, and their employment often 
leads to insanity. 

Action of Tobacco. — When tobacco is indulged in to 
any great extent it produces confusion of sounds in the 
head, with ringing in the ear, and imperfect vision, some- 
times amounting to total blindness. If it does not have 
such a powerful effect, it leaves the person nervous and 
irritable, and unfitted for manly work or mental labor or 
usefulness. Tobacco is such a deadly poison that physi- 
cians scarcely ever prescribe it as a medicine. 

Cigarettes should not be smoked by young persons, as 



164 ELEMENTARY PHYSIOLOGY. 

they are nothing but tobacco in packages of smaller size, 
and are often mixed with other articles, as opium or refuse 
matters, which are very injurious to the health. 



QUESTIONS. 

What is the cerebrospinal system ? What are the nerves? 

How many coats has the brain ? The spinal cord ? 

What is the sympathetic system ? What are its uses? 

W T hat two kinds of nervous matter are there ? Their uses ? 

What three parts has the brain? How much is the brain proper? 

What is the average weight of the brain in man and woman? 
Compared with the weight of the body ? 

What races have brain most developed ? 

What are the hemispheres of the brain ? What is the cerebellum ? 

What is the arrangement of the spinal cord ? 

What are the nerves ? Of what formed ? Their uses ? 

What is the sympathetic system ? 

How many spinal nerves are there ? How many cranial nerves ? 

What organs are supplied by cranial nerves? The fifth pair? 

What are the roots of spinal nerves ? Their action ? 

How are impressions conveyed to and from the brain ? 

What is the great central organ of sensation ? Of the will ? 

What are the duties of the two kinds of nerves ? 

What is reflex action of the spinal cord ? 

What are the duties of the medulla oblongata ? Of the cerebel- 
lum? Of the cerebrum? 

What occurs during sleep? How much is necessary ? 

What peculiarities are there in the nervous system of other animals ? 

What is the best way to keep brain and nervous system healthy? 

What is the effect of alcohol upon the brain? On the nervous 
system ? Alcoholism ? 

What are narcotics ? What is opium ? What are its effects ? 

What effect have chloral, tobacco, etc. upon the nervous system ? 



THE SENSES. 



The Senses, as they are called, are touch, taste, vision, 
hearing, and smelling. These all require special organs. 
The object of the senses is to make us acquainted with 
the world around us ; without them we would have no 
ideas of taste, odor, or sound, or the properties of bodies, 
such as we acquire through the tongue, the nose, the ear, 
the eye, and the skin. 



TASTE. 

The Organ of Taste. — The surface of the tongue and 
the mucous membrane of the mouth form together the 
organ of taste. If the lining of the mouth be injured in 
any way pain will take the place of taste. By the action 
of the teeth and salivary glands the food is brought in 
contact with the nerves of taste in all parts of the mouth. 
The impression is made on the nerves of taste, and thence 
carried to the brain, which appreciates it. 

The tongue has several important nerves and also 
muscles, w r hich move it in various directions, as in chew= 
ing or in swallowing. 

The tongue is covered with points, called papil'lce, in 
which are the delicate threads of the nerve of taste 
(Fig. 77). Some of these papillae are concerned with the 

165 



166 



ELEMENTARY PHYSIOLOGY. 




sense of touch, others with the sense of taste. The 
tongue is also supplied with little glands, which pour 
out a thin fluid to moisten the interior of the mouth. 
The tongue must be moist and the 
article soluble before there can be 
perfect taste. 

Conditions of Taste. — Solution of 
an article in water separates the par- 
ticles so that they come directly in 
contact with the tongue; but some 
articles, as metals, held in the mouth, 
have a peculiar taste without being 
dissolved. 

Articles of food are spoken of as 
sweet, sour, bitter, etc., agreeable or 
disagreeable. Substances of agreeable 
taste are generally useful ; those of 
disagreeable taste, either injurious or 
without any advantage as food. The quantity of food 
necessary to give rise to a taste is sometimes so small 
that it can scarcely be weighed on the lightest balance. 
A drop of a bitter article will sometimes give a bitter 
taste to a quart of water, but it requires a great deal of 
sugar to give a sweet taste to the same quantity of water 
The sense of taste is under the control of the will. It 
may be injured by indulgence or excess in drinking,, 
Taste is not perfect unless the power of smell is also 
perfect. If we close the nose tightly, taste is blunted 
or destroyed. As a rule, articles of food pleasant both 
to taste and smell are generally likely to agree with 



Fig. 77. — The Human 
Tongue. (Showing 
also the back part 
of the mouth.) 

a, the palate; b, tonsil; c, 
epiglottis ; d, e y f, papillae. 



THE SENSES. 167 

the stomach ; those which are not pleasant both to 
taste and smell are likely to disagree. 

Many articles taken as food in one part of the world 
are not liked in other parts. Many years ago horse-flesh 
was not eaten as food, while now there are several hun- 
dred establishments in France devoted to the preparation 
of it for food. 

Nerves to the Tongue. — Three nerves are distributed 
to the tongue : the fifth pair, from the brain, which gives 
it sensation or feeling ; the eighth pair, which with the 
fifth seems to make the taste perfect; the ninth pair, 
which moves the tongue, as in swallowing, speaking, etc. 

Organ of Taste in Other Animals. — In the higher 
classes of animals the organ of taste is very much the 
same as in man. The sense is not strongly developed in 
birds. The tongue of the woodpecker is not an organ 
of taste, but it is sharp and like a fork, with which it 
pierces insects. The parrot uses his tongue to hold the 
article he may be eating. In some reptiles the tongue is 
large and muscular. In serpents it is sharp and forked 
and moves very quickly. In the bee the tongue is like a 
little tube, through which it sucks juices from flowers. 
The tongue in some fishes does not move in the throat. 



QUESTIONS. 
What are the five senses and their objects ? 
What is the organ of taste ? What are the papillae ? 
What nerves are distributed to the tongue ? 
What effect has the sense of smell on taste ? 

What is the arrangement of the tongue or organ of taste in other 
animals? 



168 



ELEMENTAKY PHYSIOLOGY. 



SMELL. 

The Organ of Smell. — The organ of smell is the 
mucous membrane lining the nose, particularly its back 
part. The odorous properties of bodies pass into the 

interior of the nose 
in very fine particles. 
The surface is full 
of nervous papillae or 
projections. The mem- 
brane is continued up 
into the bony cavi- 
ties back of the nose, 
which open behind 
into the throat, so 
that the air can pass 

Fig. 78. — Nerves supplied to the Cavities freely through. 

of the Nose. t-» i , »i • t 

Jirfacn nostril is di- 
vided at its back part into three passages. Two of these 
communicate with cavities in the bones, thus forming 
large spaces for smell. The mucous membrane is smooth 
and velvety, lines all the cavities, and pours out mucus 
to keep the parts moist. 

The Nerve of Smell. — This is the first pair of cranial 
nerves, which divides into small branches, and passes 
through openings in the skull, and when it reaches the 
upper and back part of the nose it is scattered to be 
sent like a shower in fine branches over the upper and 
middle parts of the mucous membrane (Fig. 78). The 




THE SENSES. 169 

fifth pair sends branches to the nose, and gives general 
sensibility to it, and perfects the sense of smell. 

The shape of the nose supplies a funnel in which to 
collect odorous particles. 

Odors. — Odors are separated from bodies by rubbing, 
heat, light, chemical action, moisture, etc. The effect of 
moisture is shown in the smell to be noticed after a shower 
in a garden of flowering plants. For perfect smell, the 
nose must be thoroughly open, the membrane healthy 
and moist, the nerve and brain perfect. 

The particles that give odor need not be placed close 
to the nose. The smell of cinnamon has been noticed 
two hundred miles from land. 

How Smell is Effected. — The air containing the odor 
is drawn into the nose, so as to carry it as far as possible 
up that organ to reach the nerve of smell. The mucus 
on the lining membrane stops the progress of the parti- 
cles, so that they can affect that nerve. 

Through the nose and its cavities, in respiration, the 
air passes to the lungs, and if there be anything offensive 
in the air we breathe, the nose warns us in regard to it. 

Sense of Smell in Animals. — Animals which have the 
greatest development of the nerves of smell have the 
strongest instincts of scent, as it is called. Birds search- 
ing for food generally use their sight more than their smell. 

The scent of animals, as of the pointer and bloodhound, 
depends on their power to detect by the nose the odorous 
particles given off by other animals. These, being heavy, 
are generally noticed near the ground, and this is why 
scenting dogs apply the nose as low as possible. 



170 



ELEMENTARY PHYSIOLOGY. 



QUESTIONS. 

What is the organ of smell? The object of the sense of smell? 

What membrane lines the cavities of the nose ? 

What is the nerve of smell ? 

What other nerves go to the nose ? 

For perfect smell what organs must be perfect ? 

How is smell effected ? 

What is the condition of this sense in other animals? 

What does the scent of animals depend upon ? 



TOUCH. 

The Organ of Touch. — In the skin are myriads of 
nervous points called papiVlcv — in greater numbers wher- 
ever touch is most acute, as in the fingers. Here are 
also small firm bodies, closely connected with the nerve, 




Fig. 79. — Papilla of the Skin of the Hand (greatly magnified). 

1, papillae with blood-vessels ; 2, papillae with touch-body ; 4, o, large papilla? ; 6, 7, 
vessels beneath or in papillae ; 8, nerves beneath papillae ; 9, 10, 11, touch-bodies. 

called touch-bodies, which render touch still more acute 
(Fig. 79). The sense of touch is most perfect in the 
hands. Here there are 20,000 papillae to the square 



THE SENSES. 



171 



inch. Beneath the skin is a layer of fat, which gives the 
figure its round appearance. 

The papillae vary in size, being usually about xcToth of 
an inch long and yroth °f an mcn broad, well supplied 
with capillary blood-vessels, as in the fingers (Fig. 79). 

The Skin. — The skin protects the parts beneath, and 
also gets rid of some watery and fatty matters. The outer 
layer, the epider'mis (from Greek words meaning " upon 
the skin "), is thick where it is pressed upon, as in the 
fingers or heels, and thin over the lips. It has no nerves 
or blood-vessels, and therefore any pain in the skin, or 
any bleeding from it, must come from the layer of the 
skin beneath it, the cu'tis (Latin for " skin "), der'ma, or 
true skin, which has in it a great many vessels and nerves. 

Sweat-Glands (Fig. 
81). — The sweat or per- 
spiration is obtained from 
the blood by glands in 
the skin. Each gland is 
a tube turned upon itself, 
and empties on the skin. 
The sweat-glands num- 
ber nearly 3000 in each 
square inch of skin on 
the palm of the hand or 
the sole of the foot, and 
in the whole body they 
number about 7,000,000. If all the sweat-glands were 
placed end to end they would extend more than three 
miles. The sweat from these glands is not generally 




Fig. 80. — Surface op the Palm of 
the Hand (slightly magnified). 

1, 1, 1, opening of ducts of sweat-glands ; 
2, 2, 2, grooves between the papillae of the 
skin. 



172 



ELEMENTARY PHYSIOLOGY. 



seen; it is carried off as a vapor. It is noticeable 
after exercise or in hot, moist weather. The amount 
poured out in twenty-four hours is about two or three 
pounds. 

Sebaceous or Fat-Glands. — The skin is kept soft by 

fatty matter poured 
out on its surface 
by seba'ceous glands 
(from a Latin word 
meaning " suet "). 
There are a great 
many of them on the 
face and the top of 
the head, where they 
moisten the hair. 

Hair (Fig. 81).— 
A hair is not so sim- 
ple as it looks ; it has 
a shaft above the 
skin and a root with- 
in it. Whfen a hair 
grows to excessive 
length it may split 
into fibres like a 
painter's brush, 
which will become 
brittle and break off. This is not likely to happen if 
there is enough fatty matter to keep the hair from be- 
coming dry. 

The hair partially protects the head from injury or 




Fig. 81, — Section of Skin (magnified). 

1, epidermis ; 2, dermis ; 3, hair-follieles ; 4, color- 
ing matter; 5, touch-bodies; 6, sweat-glands; 7, 
fat-cells. 



THE SENSES. 



173 



from excessive heat or cold. The eyebrows and eye- 
lashes protect the eyes from dust or other matter that 
might injure them. The color of the hair depends on 
the presence of coloring-matter in the cells at the roots 
of the hairs. A hair becomes gray or white because 
there is not enough coloring-matter secreted. 

The nails aid in touch, and give a support for the ends 
of the fingers. Horns, feathers, hoofs, scales, bristles, 
etc. have similar uses. 

Color of the Skin. — This depends on the deposit of 
coloring-matter in the deeper layer of the skin. Black 
coloring-matter is found in the negro, red in the 
Indian. 

The Hand. — This is in man 
the principal organ of touch. 
By it he learns shape, weight, 
hardness, etc. Its joints and 
tendons (Fig. 82) admit of 
great variety of motion. The 
thumb is especially character- 
istic of man. 

The Sensation of Touch. — 
The sensation differs with the 
nature of the body touched, 
the temperature, etc. It some- 
times deceives us. If, for in- 
stance, we place a marble be- 
tween the fingers, as in Fig. 83, we feel only one marble ; 
but if we afterward cross the two fingers we think we feel 
two marbles. A separate impression is made on each 




Fig. 82. — Tendons of Hand. 



174 



ELEMENTARY PHYSIOLOGY. 



finger in spite of our knowledge that only one marble 
is there. 





Fig. 83. — An Illusion of Touch. 

Sense of Touch in Other Animals. — In most of the 
higher classes of animals the tongue, lips, and snout are 
the chief organs of touch. In many insects the outer 
covering of the body is thick and shell-like, and some 
of them have near the mouth movable feelers, which can 
be directed toward any object. The scales of fishes in- 
terfere with their sense of touch. The whiskers of the 
cat and of other animals assist them in their touch. 

Hygiene of the Skin. — The health of the body is im- 
proved by attention to two very important matters — 
clothing and bathing. 

The clothing must be clean, and not worn so long as 
to be soiled with waste matter from the skin, which will 
otherwise remain in the system to exert an injurious and 
perhaps poisonous effect. Clean and frequently-changed 
underclothing, as. it comes directly in contact with the 



THE SENSES. . 175 

skin, is especially desirable, as it readily absorbs moisture 
from the skin. Clothes worn during the day and bed- 
clothes used at night should be well aired, and thus 
purified. 

Bathing. — Bathing the surface of the body, with fric- 
tion from the towel, removes dirt or dust from the skin, 
and clears it of any matter left as a deposit after evapora- 
tion of the watery particles from the sweat-glands and the 
fatty matter from the sebaceous glands. A cold bath 
taken daily will, as a rule, agree with those of strong 
constitutions, but it should be immediately followed with 
active friction with a coarse towel until a glow is pro- 
duced, and a certain amount of after-exercise must be 
practised. 

A chill after a cold bath shows that it does not agree 
with the bather. Those who are feeble should use mod- 
erately warm water, say once or twice a week, and for a 
short time only ; but the skin should be thoroughly dried 
and rubbed until it becomes warm. Sea-bathing has a 
still more stimulating effect. 

Perfumery is sometimes used to conceal the odor from 
an unclean body, and cosmetics to give artificial color to 
the face ; but many of these articles are made up of 
poisonous matters, such as lead, and few are perfectly 
harmless. Soap is decidedly better for the removal of 
dirt from the skin, and perfumes, if employed at all, 
should follow its use. 

A bath should not be taken after a full meal, about 
three hours being allowed to elapse. Early morning is 
the best time for a cold bath, but any one not accustomed 



176 ELEMENTARY PHYSIOLOGY. 

to it should begin at a higher temperature — say 65° or 
70°— and gradually reduce it. A stay in the bath often 
to twenty minutes is sufficient, and even at the seashore 
it should not be protracted to a much longer period. The 
body should not be chilly when entering the water. 



QUESTIONS. 

What is the organ of touch ? What are the papillae ? Touch-bodies ? 

What is the use of the skin ? What fluids pass through it ? 

What are the layers of the skin called ? 

What is the size of the papillae ? 

From what is sweat derived ? How many sweat-glands in the body ? 

How much sweat is secreted in twenty- four hours ? 

What are the sebaceous glands ? What do they pour out ? 

Into what parts is a hair divided ? 

What does the color of the hair depend on ? 

What does the color of the skin depend upon? 

What are the chief organs of touch in other animals? 

What is said of clothing ? Of bathing ? 

What rules are best as to taking baths ? 



VISION. 

The Organ of Vision. — By vision we judge of light and 
color, and of the shape, size, distance, and properties of 
objects around us. Sight or vision depends on the optic 
nerve — the second pair of nerves — and an organ, the eye, 
conveying light to it. 

The parts necessary for sight are contained in the globe 
or ball of the eye. These parts, as well as the nerve of 



THE SENSES. 



17? 




vision and the brain 
itself, must be perfect. 
The optic nerves as 
they pass from each 
side to the eyes cross 
like the lines in the 
letter X. 

Protection of the Eye. 
— The eyelids, eye- 
lashes, and eyebrows 
shield the eye from ex- 
cessive light and pre- 
vent dust from irritat- 
ing it, while the tears 
poured over the eye 
and the sebaceous mat- 
ter keep it moist. 

The Tears. — The tears are poured out by the lach'rymal 
gland (from a Latin 
word meaning " a 
tear ?> ), one on each 
side, above the outer 
part of each eyebrow 
(Figs. 84, 85). The 
tears are being poured 
out at every moment 
of our lives. 

They keep the sur- 
face clear and transpa- 
rent, and give lustre to the eyes. 

12 



Fig. 84. — Section of the Eye. 

1, 2, 3, 4, 5, muscles of the eyeball ; 6, lachry- 
mal gland, with its ducts, 7, 8, 9. 




Fig. 85.— The Eye. 

a, canal for passage of tears iuto the nose ; 6, 
iris ; c, position of lachrymal gland ; d, pupil ; 
e, mucous membrane. 



The tears then pass 



178 



ELEMENTARY PHYSIOLOGY. 



into the inner corner of the eye, and thence by a little 

canal into the nose. 

The Orbits.— The eyeball 
is placed in a deep bony space 
or cavity — the socket or orbit 
Some fat in this cavity fur- 
nishes a cushion for the eye- 

Fig. 86 Sebaceous Glands of the ball. 

Eyelashes (slightly magnified). j he Eyelids .— The eyelids 

act like a curtain to the eye ; they are covered on the 





Fig. 87. — The Eye. (A vertical section through the middle of the eyeball.) 

1, cornea; 2, aqueous humor; 3, pupil; 4, iris; 5, lens; 6, ciliary processes; 7, 
canal around the lens; 8, sclerotic coat; 9, choroid; 10, retina; 11, vitreous 
humor ; 12, optic nerve ; 13, 14, 15, muscles of the eyeball and of the eyelid ; 
16, 17, eyelids. 

outside by skin, on their inside by delicate mucous mem- 
brane, which is reflected over the front of the ball. 
The Eyelashes. — The eyelashes and lids regulate the 



THE SENSES. 179 

amount of light to the eye. Little sebaceous or fatty 
glands (Fig. 86) pour out an oily fluid on the lids, so 
that they do not stick to one another, and also prevent 
the tears from overflowing the cheek. 

Transparent Parts of the Eye (Fig. 87). — The front 
part of the eye, shaped like a watch-crystal, acts like a 
window, and is called the cor'nea, from its looking like 
a horn (cornu, "horn") (Fig. 87, 1). Behind this is the 
anterior chamber (front apartment), containing a watery 
fluid called the aq'ueous or watery hu'mor (Fig. 87, 2). 
Behind this is the only solid part of the eye, the crys- 
talline lens (Fig. 87, 5), convex on its front and back sur- 
faces. It is about a quarter of an inch thick, and is per- 
fectly transparent. 

Farther back is a transparent, jelly-like material, the 
viVreous or glassy humor, resembling melted glass, placed 
in the posterior chamber (back apartment), and occupying 
about two-thirds of the eyeball. 

Coverings of the Eye. — The eye has three coverings or 
coats. The outer one, giving shape to it, is the sclerotic 
(Fig. 87, 8) (from a Greek word, meaning " hard "). 
The muscles moving the eyeball are fastened to it. It 
is the " white of the eye." The next coat is the eho'roid 
(Fig. 87, 9), a black, opaque membrane, with numerous 
vessels passing into it, and this coat absorbs unnecessary 
rays of light, and thus prevents confusion of sight. 

The third and last membrane, the reVina (Fig. 87,10), 
lines the back part of the eyeball. It is a spreading out 
of the optic nerve, and is therefore sensitive to light. 

In the front part of the choroid is a movable curtain, 



180 ELEMENTARY PHYSIOLOGY. 

the i'ris (Figs. 85, b ; 87, 4), with muscular fibres, which 
dilate and contract the pupil — the opening in the centre 
of the iris (Figs. 85, d; 87, 3). The dark coat of the 
choroid acts like the black coating we see in telescopes : it 
shuts out unnecessary rays of light, and thus prevents 
confusion. The color of the choroid as seen through 
the iris gives color to the eye — as blue, hazel, gray. 
Dark eyes, for instance, depend on the deep color of the 
choroid ; light eyes, on a pale and colorless choroid. The 
amount of light passing through the pupil may be made 
smaller by contracting the iris. When the light is not 
sufficiently bright the pupil will enlarge itself. The size 
of the pupil has much to do with the brilliancy of the eye. 

There are six muscles which move the eyeball, and 
they act independent of the will, although we have the 
power also of moving the eye in different directions. 

Light. — The cause of vision is the action of light on 
the retina. We suppose that an elastic medium occu- 
pies all space, which is excited into rapid waves by the 
sun or any other luminous body. These waves travel 
nearly 190,000 miles a second; the light of the sun — 
which celestial body is said to be 95,000,000 miles away 
from us — takes over eight minutes to reach us. 

The Course taken by the Rays of Light. — Light (Fig. 88, 
c d) passing through a transparent uniform medium, a b, 
like air, proceeds in a straight line. If it comes in con- 
tact with any other transparent body that is denser and 
heavier, such as water, it is either reflected, e h — that is, 
turned back in its course — or it is broken or refracted, e g. 

Rays of light striking upon the eye pass first through 



THE SENSES. 



181 



the cornea, which is convex, and therefore refracts them ; 
then through the aqueous 
humor, which does not 
cause much change ; 
they next strike upon 
the iris, which reflects 
those falling on its sur- 
face, and only such rays 
as pass through the pu- 
pil reach the retina. FlG - 88.— Refraction of Light. 

They next come in contact with the crystalline lens 
(Fig. 87, 5), which refracts them ; and then through the 
vitreous humor, falling at last on the retina, producing 
upon it an image of the object. 

The Image on the Retina. — This image (DE, for in- 
stance, Fig. 89) is reversed ; that is, upside down : and 







Fig. 89. — Formation of an Image on the Retina. 

yet the brain sees the object in its natural position. 
Each retina receives an image, but the brain sees only 
one. 

Far Sight and Short Sight. — In the healthy eye parallel 
rays (Fig. 91, a) from a distance must come to a focus, 
or central point (x), on the retina, or the image will be 



182 ELEMENTARY PHYSIOLOGY. 

indistinct. In short-sighted persons (Fig. 91, b) they 




Fig. 90. — Inverted Image on the Retina shown in the Bullock's Eye. 

come to a focus (x) in front of the retina. In the far- 
sighted (Fig. 91, e), 
they come to a focus 
(x) behind the retina. 
Short - sighted persons 
must use concave glasses, 
to remove the focus far- 
ther back to the retina. 
Far - sighted persons 
must use convex glasses, 
to bring the focus far- 
ther forward. 

Impression on the Ret- 
ina. — An impression on 
the retina generally lasts 
from -^o th to ^th of a 
Fig. 91. second. Take a round 

A, natural sight; B, short sight; C, far sight, piece of Card having 

one side black and the other white, and turn it rapidly, 




THE SENSES. 183 

when only continuous dark bands will be seen. If a red 
spot be painted on the face of the card, it will appear 
like a red band when it is turned rapidly, showing that 
the impression is continuous. Each impression is con- 
founded with those which follow it. 

There is a spot on the retina, the blind spot, at the en- 
trance of the optic nerve, at which light and color are 
not appreciated. To prove this, shut the left eye ; with 
the right eye look steadily at 

the cross on this page (Fig. T • 

nnx i .i n i i Fig. 92- -Experiment in re- 

92), and then move the book ^^^^a^^^^. 

/ ? GARD TO THE " J3LIND OPOT. 

toward the eye and away from 

it. The round spot will disappear, just as soon as the 

image from it falls directly on the blind spot, which 

although small, is large enough to cause a figure of a 

man to disappear at a distance of about six: and a half 

feet. 

In the centre of the retina is a yellotv spot very sensi- 
tive to light. When we read a book we bring each word 
in the text opposite the yellow spot, the centre of vision. 

Perception of Colors. — The eye also perceives colors, 
of which there are seven elementary ones — violet, indigo, 
blue, green, yellow, orange, and red (remembered by the 
word " vibgyor" which contains the first letter of each 
color). Some persons cannot tell one color from another, 
and are therefore said to be color-blind. Red and green 
are the most confusing colors. In all parts of the world they 
now regularly examine the eyes of locomotive engineers 
and signal-men, as, if color-blind, they might mistake the 
color of the signals and thus cause terrible accidents. 



184 ELEMENTARY PHYSIOLOGY. 

Vision in Other Animals. — In some low forms of ani- 
mals the eyes are merely dots to distinguish light from 
darkness. In some fishes, and in some other animals 
that live both on land and in water, the eyes are covered 
with a skin. In some animals, as the tortoise, there is a 
movable membrane. In many birds it can be drawn 
over the surface of the eye to protect it from light or 
foreign bodies. 

In some animals the choroid is absent and the eye 
looks white or metallic. In the cat and the lion a por- 
tion of the choroid is covered with a bluish layer shining 
like metal, so that the light is strongly reflected and the 
eyes seem like balls of fire. In cats and crocodiles the 
pupil is longer up and down than it is from side to side. 
In animals which seek their prey by night the eyes are 
usually large ; in the daytime the pupil appears almost 
like a buttonhole, while at night it is round, as in 
man. 

Insects and such animals as crabs and lobsters have 
compound eyes, made up of tubes, which go off from a 
centre like spokes of a wheel placed closely together. 
There are sometimes 10,000 to 20,000 of these tubes in 
a single eye, each one an eye itself, and all packed in a 
space of a small fraction of an inch. The ant has 50 of 
these eyes, the fly 4000, the butterfly more than 17,000. 
They seem to have eyes for every direction. 

Eyes are not always placed alike, on opposite sides. 
Insects living entirely in dark caverns or deep wells are 
devoid of organs of sight. Birds are far-sighted ; fishes 
are near-sighted. 



THE SENSES. 185 

Hygiene of the Eyes. — Every care should be taken to 
preserve the sight in as perfect condition as possible. It 
may be well, therefore, to give rules for the avoidance of 
the usual causes of injury to vision in every-day life. 

Never look or gaze at objects that are intensely bright, 
as a full gas-jet or electric light ; especially at the sun 
itself, even when it may be partly or wholly eclipsed. 
Never strain the eyes to read or sew when the light is 
feeble or flickering. Do not use a lamp with a shade or 
globe upon it which renders the light intensely white to 
the eye ; the light from it should be modulated with a 
colored paper or silk shade. When the day is dying out 
do not attempt to read or sew up to the very last moment 
of visible light, when the eye can scarcely see the objects 
before it. Do not attempt to read printed matter, espe- 
cially fine print, while riding in a carriage, street-car, or 
train ; the effort of the eye to accommodate itself to a 
changing focus will fatigue and injure the delicate nervous 
coat of the eye, and probably lead to defective power of 
that organ. 

Never read a paper or letter with the light shining 
directly upon it ; it is better that the light should come 
from the side or back of the person, and not from the 
front. The eyes should not be used to the point of 
extreme fatigue; they need rest after work, as does 
every other organ of the body. If the eyes are used 
continuously and intently on one kind of work, such as 
sewing, they may sometimes be rested by changing their 
occupation for a while, as by reading. Never allow them 
to be strained over very fine type ; it is better to lay aside 



186 ELEMENTARY PHYSIOLOGY. 

a book entirely than to force the eyes to labor over it& 
text with such effort as the reading of small type will 
call for. 

Do not continue to use an eye that is inflamed, de- 
fective, or feeble without seeking good medical advice, as 
its continued employment will only increase the mischief 
already existing, and may at last produce blindness or 
impaired vision. Do not rub the eye to remove dust or 
other particles from it ; these can generally be seen and 
taken away by carefully applying the corner of a soft 
handkerchief folded. Do not pull the eyelids in hopes 
of bringing to the eye enough tears to wash out the 
offending substance. 

Wash the eyes always with cool water; avoid using 
water for this purpose that is very hot or very cold. Do 
not read while lying in bed or on a sofa, as some of the 
muscles of the eyeball are overstrained by such an act. 

Effect of Alcohol and Tobacco on Vision. — When alco- 
hol is used as a drink it is apt to cause inflammation or 
congestion of the eyeball and of the lining membrane of 
the eyelids. Weakness of vision is quite well known as 
a disease of drinkers, and this is apt to last as long as 
the cause — alcoholic drinking — is indulged in, and at last 
the whole structure of the eye becomes changed and the 
nerve of sight wastes away, and perhaps blindness may 
result. 

Tobacco produces confusion of sight, with specks before 
the eyes, and deeply-seated pain. The nervous coat be- 
comes so seriously affected that the object that impressed 
it is seen long after the eye has ceased to look at it. 



THE SENSES. 187 

QUESTIONS. 

What is the nerve of vision ? What parts protect the eye ? 

What effect have the tears and sebaceous matter ? 

What gland secretes the tears ? When does this take place ? 

What is the socket or orbit of the eye ? What are the eyelids ? 

Of what use are eyelashes? How are their edges greased? 

What is the cornea? The anterior chamber of the eye? The 
crystalline lens? 

What are the other transparent parts of the eye ? 

What are the three coverings of the eye ? W T hat is the nervous coat ? 

Through what transparent parts must light pass to reach the retina? 

What is the iris ? The opening in its centre ? Its uses ? 

What muscles are attached to the sclerotic coat? 

W T hat kind of a membrane is the choroid ? Its uses ? 

What part of the eye gives color to the eyes ? 

What kind of a membrane is the retina ? Its uses ? 

How is the eyeball moved ? 

What is the cause of vision ? The theory of light ? 

How fast does light travel ? 

What is reflection of light? Refraction? 

What effect has the cornea upon light ? The iris ? The lens ? 
The pupil? What is the position of the image on the retina ? 

What becomes of the parallel rays of light in the healthy eye ? In 
the near-sighted eye ? In the far-sighted eye ? 

How can short sight be corrected ? Far sight ? 

How long does an impression on the retina last ? 

What is the blind spot of the retina? What effect on vision? 
What is the yellow spot ? What effect on vision ? 

What are the seven elementary colors? 

What is color-blindness? What colors are generally confounded ? 

What peculiarities of vision are noticed in the lower animals ? 

Is the pupil always round, as in man ? 

What are the compound eyes of flies, butterflies, etc. ? 

What are some of the rules for taking care of the sight ? 

What effect have alcohol and tobacco on vision ? 



188 



ELEMENTARY PHYSIOLOGY. 



HEARING. 

The Organ of Hearing. — The organ of hearing is the 
ear. It consists of three parts — an outer ear, the middle 
ear, and an inner ear, in which is the nerve of hearing. 

The Outer Ear (Fig. 93) consists of the projecting part 




Fig. 93.— The Ear. 

a, external auditory canal or tube ; b, Eustachian tube; /, oval window in tJie 
vestibule; o, round window; d, e,/, little bones of the ear; i, middle ear; k, 
vestibule ; /, semicircular canals ; m, cochlea ; n, membrane of the drum. (All 
the inner parts are here larger than natural.) 

on the side of the head and a canal or tube (Fig. 93, a) lead- 
ing inward, the aud'itory canal or tube, closed at its inner 
end by the membrane of the drum of the ear (Fig. 93, n). 




THE SENSES. 189 

The Middle Ear, or drum, is filled with air, and com- 
municates with the throat by the Eustachian tube (pron. 
UsefoMan), named after the anatomist Eustachius, who 
first described it. 

The Inner Ear is called the lab'yrinth, because it is so 
intricate. In the inner ear is the nerve of hearing. 

The bony labyrinth is made up of apartments and 
canals hollowed out in the bone (Fig. 93). In it is a 
small quantity of fluid. In 

this labyrinth, and sur- ^f ^ P" Jlll W 

rounded by this fluid, is 
the membranous labyrinth, 
in which is the nerve of 

hearing, bathed in another FlG - 94.— The Cochlea (represent- 
T , ing its spiral structure). 

fluid. In the membranous 

labyrinth are parts called the vestibule, with the semi- 
circular canals (Fig. 93, h, I). In each canal are fine 
long threads like hairs, which are part of the nerve of 
hearing. There is also a part called the coch'lea ("a 
snail-shell"), Figs. 93, m; 95, A, D), a portion of which 
is winding like a staircase (Fig. 94). 

How Sound is Heard. — The outer ear collects the waves 
of sound and forwards them to the membrane of the 
drum. The familiar habit of applying the hand behind 
the ear when we desire to increase our capacity for hear- 
ing is practised with a view of collecting the vibrations 
or waves of sound, so that they will pass in greater quan- 
tity and force into the outer ear. The external audi- 
tory canal (Fig. 93) is protected from injury from insects 
and foreign bodies by a form of secretion called ear-wax, 



190 



ELEMENTARY PHYSIOLOGY. 



poured out by certain glands called cey^u'minous glands 
(from ceru'men, " wax ") on its surface, and by the hairs 
that grow along the canal. The middle ear, or drum, has 
several small bones connected with it, moved by very small 
muscles, which vibrate and render the membrane of the 
drum tight or loose according to the intensity of the sound. 
The vibrations of sound are forwarded to the inner 
ear, partly through the air in the middle ear and partly 

B 




Fig. 95. — Interior of the Inner Ear. 
A, D, cochlea ; B, B, semicircular canals ; C, vestibule. 

along the chain of little bones, which are called, from 
their shape, the hammer, the anvil, and the stirrup (Fig. 
93, d, e,f). The vibration of the little bones is com- 
municated to the fluid in the labyrinth, and thence to the 
hair-like ends of the nerve of hearing, through which 
the impression is carried to the brain. For perfect hear- 
ing both the brain and the nerve of hearing must be in 
a healthy condition. 



THE SENSES. 191 

Sound. — The lowest sound that can be heard is said to 
be that made by a pith-ball, about -^ of a grain in 
weight, falling upon a smooth piece of glass from a 
height of 2V of an m ch at a distance of 3J inches from 
the ear. A certain number of vibrations is necessary to 
produce a tone, otherwise sound will not be heard. The 
lowest limit is said to be 30 vibrations a second, the 
highest between 30,000 and 35,000. 

The two ears hear a single sound, and the brain ap- 
preciates but one sound. Sound is transmitted, as light 
is, by waves. 

The Sense of Hearing in Other Animals. — All the 
higher animals have outer ears, which in some of them 
can be turned in a direction to catch the sound. Birds 
do not have any outer ear, but in some of them the 
drum communicates with cavities in the bones of the 
skull, which act like a sound-board of a piano. The 
little ear-stones in the inner ear are noticeable in fishes, 
some of which have them as the whole organ of hearing, 
in addition to a nerve. 

Hygiene of the Hearing. — Avoid draughts of cool or 
damp air, which can affect the ear either by the Eusta- 
chian tube from the throat or directly through the outer 
ear. Do not strike any one on the ear or on the side of 
the face, as the drum of the ear may suffer, perhaps be 
ruptured, or the little bones of the middle ear may be 
injured, and deafness result. Be careful in picking 
out wax from the ear ; it not only protects it from in- 
sects or foreign bodies, but in the effort to dislodge it the 
person may injure the membrane of the drum of the ear. 



192 ELEMENTARY PHYSIOLOGY. 

Loud sounds, such as the firing of cannon, explosions, 
etc., have been known to affect the hearing by bursting 
the membrane of the drum. As it is better to open a 
window before an expected explosion or cannonade, so as 
to break the effect of the vibration, so is it well to open 
the mouth in order that the Eustachian tube from the 
throat may also be open, and the whole force will not 
then be spent upon the membrane of the drum. 

Deaf persons, of course, fail to hear the voices of 
friends, the sounds of music, etc., and as these are great 
sources of pleasure, we should avoid, as much as possible, 
all influences that are apt to lead to deafness. The outer 
canal of the ear should never be violently washed out 
with a syringe or rudely wiped out with a wash-rag ; 
force is never necessary. Never pick or dig into the ear 
with hair-pins, toothpicks, pins, or any other articles, as 
the membrane of the ear may be pierced by them. 

Oily and greasy matters dropped into a healthy ear 
often irritate it, and should not be recklessly used when 
the ear is inflamed. Diving into the water or dropping 
into it from a height will often injure the ears or affect 
the hearing. Do not throw very cold or very hot water 
into the ears. 

Alcohol and tobacco injure the sense of hearing. Al- 
cohol may produce an inflamed condition of the throat, 
and the inflammation may travel up the Eustachian tube 
into the middle ear, and produce deafness. Tobacco may 
produce catarrh of the throat and nose, and disease of the 
ear may follow. It frequently leads to confusion of 
sounds in the ear, and the extremes of sound — such as 



THE SENSES. 193 

loudness and softness — which are the test of delicacy of 
hearing in the healthy ear, are not properly appreciated 
by the organ of hearing. Some of this eifect may be due 
to the fact that the brain itself is confused by the tobacco 
or the alcohol, and rendered unfit for the appreciation of 
sounds. 



QUESTIONS. 

Of what three parts does the organ of hearing consist? 
What parts compose the external ear ? The middle ear ? 
What is the labyrinth ? Of what parts is it composed ? 
What are the little bones of the ear called? Their uses' 
What is the cochlea? 

How does sound reach the inner ear ? The brain ? 
What parts must be perfect to ensure perfect hearing? 
What is the lowest sound that can be heard ? The lowest and high- 
est number of vibrations of sound that can be heard by the ear? 
W T hat peculiarities of the ear in other animals ? 
What are some of the rules for taking care of the hearing? 
What effect have alcohol and tobacco on the hearing? 
13 






VOICE. 



The Organ of Voice. — Voice is produced by vibration 
of the vocal cords in the larynx while the air is passing 
through it. The parts concerned in its production are 

the larynx, windpipe, 
lungs, mouth and nose, 
and muscles of breath- 
ing. 

The Larynx. — The 
larynx (Fig. 96) is sit- 
uated in the front of the 
neck ; it is more promi- 
nent in the male, in 
whom it is commonly 
called the " Adam's ap- 
ple," as if the apple 
which Adam ate had 
stuck in his throat. The 
mucous membrane of the 
mouth and throat passes 
down into the larynx and 
windpipe. The larynx is 
made up of four cartilages, movable upon one another, 
united by ligaments, and having muscles attached. 
The Vocal Cords.— Inside the larynx are two triangu- 

194 




Fig. 96. — The Larynx (front view). 
1, 2, cartilage ; 3, windpipe ; 4, ligament. 



VOICE. 



195 



lar spaces (Fig. 97). The upper space has at the side 

two folds of mucous membra ne, the upper, or false vocal 

cords; the lower one has at the side two folds, the lower , 

or tame vocal cords. 

The vocal cords are 

perfectly free to 

move, and are only 

separated from 

one another about 

a third of an 

inch. 

Muscles of the 
Larynx. — The mus- 
cles concerned in 
the production of 
voice either tighten 
the vocal cords or 
separate the carti- 
lages from one an- 
other, so as to open 
the glottis (Fig. 97, 
5), as the space be- 
tween the lower vo- 

. Fig. 97. — Interior of the Larynx. 

cal cords is called, , , ,*'«-, 

7 1, upper or false vocal cords ; 2, lower or true vocal 
Or bring theni tO- cords ; 3, epiglottis ; 4, thyroid cartilage ; 5, ver- 
gether tO Close the tical section of glottis; 6, 7, cartilages; 8, muscle 
between cartilages ; 9, windpipe. 

glottis. 

How Voice is Produced. — To produce voice, air must 
pass from the lungs through the windpipe into the 
larynx, cause a vibration of the vocal cords, and pass 





196 ELEMENTARY PHYSIOLOGY. 

out through the mouth and cavities of the nose (Fig. 23). 
This is under the influence of the will ; otherwise voice 
would be produced every time we breathe. The lower vocal 
cords (Fig. 97, 2) are the parts directly concerned in voice. 
To illustrate the passage of air through the glottis : 
Take two pieces of bladder or India-rubber and stretch 
them over the end of a tube (Fig. 98), so 
that each shall cover rather less than the 
opening, a space being left between them. 
If air be forced upward through such a tube 
by bellows a sound will result if the open- 
ing be not too wide. If the membranes be 
Fig. 98.— Plan tighter or looser, the sound will vary in 

of the Glottis. , 

character. 

Some writers describe the larynx as being like a flute, 
the vibrations being caused by air passing through ; oth- 
ers speak of it as a stringed instrument, on account of the 
vocal cords. Most writers think it is more like a reed 
instrument, such as a clarionet. The larynx is more de- 
veloped in the male than in the female, and hence his 
voice is stronger. 

Quality of Voice. — Every person has his own quality 
of voice, which distinguishes him from every one else. 
In the female the larynx is more cartilaginous than in 
the male. The change of voice in boys twelve to four- 
teen years old is due to the fact that the ligaments and 
the opening of the larynx then become enlarged. 

Whispering is the giving of slight voice to the air 
breathed out; whistling is caused by dividing the air 
as it passes through the lips. 



voice. 197 

The Singing and the Speaking Voice. — The voice in 
singing differs from the ordinary voice in speaking by 
being made up of distinct musical tones, following in 
regular order. Fig. 99 shows the ordinary average of 
the singing voice. The deepest male voice is the bass, 
the highest the tenor ; the baritone occupies a place be- 
tween these tw r o. The lowest female voice is the con- 
tralto or alto, the highest the soprano, and the mezzo- 
soprano occupies a place between them. 

The singing voice is generally from the larynx — 
chest-voice it is then called — but sometimes also from 




Fig. 99. — Range of the Singing Voice. (The figures denote the different 

octaves.) 

the throat. The laryngeal voice is usually an octave 
higher in woman than in man. The range of the human 
voice is generally considered to be three octaves, say from 
low fa or fa x (generally known as F x on the scale of the 
piano), representing 174 vibrations a second, to high sol 
or sol 4 , representing 1566 vibrations. 

The true vocal cords in men are longer than those of 
women in the ratio of 3 to 2, so that the male voice is 
stronger and lower in pitch. 

Sounds are sometimes produced that seem to come 



198 ELEMENTARY PHYSIOLOGY. 

from parts deep down in the chest, by ventril'oquism, as 
it is called, which really means " speaking from the 
stomach." The man thus manages his natural voice so 
as to mislead his hearers. 

The muscles regulating the vocal cords are only about 
three-quarters of an inch long, and all the different mu- 
sical notes are produced by their action. They can be 
varied to a movement of 1-1 200th to the l-12000th of 
an inch. 

The Formation of Language.— Speech is a series of 
sounds to convey ideas, and is under the control of the 
will. A parrot may speak distinctly, but its brain does 
not appreciate the meaning of what it says. Before lan- 
guage was formed, words were derived from familiar 
sounds, such as cries of wild beasts, notes of birds, etc. 
The names given to some sounds, as hissing, humming, 
snoring, grunting, whistling, wind, etc., convey as nearly 
as possible a notion of the sound itself. The word 
" cuckoo," which is the cry of the bird, is very much 
the same word in Greek, Latin, German, Dutch, French, 
and other languages. 

The Voice and the Hearing. — The vocal organs of a 
child may be perfect, but if he has been born deaf he cannot 
use words to express his ideas. He cannot repeat sounds 
that he has never heard, and is therefore dumb as well 
as deaf. 

Hygiene of the Voice. — The proper exercise of the 
voice is dependent upon a healthy condition of the 
throat and nose, as well as of the larynx itself. Changes 
of temperature, especially from hot to cold, exposure to 



voice. 199 

wet or to sudden draughts of air, changes of clothing, and 
many other causes, produce sore-throat, cold in the head, 
pain in the chest, or lung trouble. Whatever interferes 
with the action of the lungs must affect the voice in its 
fulness or quality. It is our duty to shun all such in- 
fluences as we know will generally produce these effects. 

We must avoid exposure to cold or to draughts when 
the body is overheated. If subject to sore-throat, we 
must wear such articles of underclothing — woollen or 
silken goods, for example — as the season or temperature 
require, and not change them by the almanac only. In 
going from a warm, crowded room into the open, cold 
air w T e must guard the mouth against the change for a 
few moments, so as to avoid the shock to the throat, by 
which hoarseness or loss of voice may be produced. Do 
not muffle the throat with wraps or scarfs ; they make 
one more liable to catch cold, especially if accidentally 
left off. 

As respiration through the nose is the natural, easy 
way of breathing, it is our duty to inquire, when chil- 
dren breathe through the mouth almost entirely — and 
especially w r hen the voice is distinctly changed by such 
an act — whether there does not exist some obstruction, 
such as enlarged tonsils or a swollen condition of the nose 
itself. Breathing through the mouth produces dryness 
of the throat, perhaps inflammation, and the air is not 
warmed for healthy purposes, as it is when it passes 
through the moist nasal passages. Particles of dust can 
also be breathed much more readily through the mouth 
than the nose, and these may become attached to the del- 



200 ELEMENTARY PHYSIOLOGY. 

icate cords of the larynx, and thus produce thickening 
and huskiness of the voice. 

In singing, the voice should not be forced beyond its 
limit or strained to produce certain effects, as high or 
low notes, which require too much effort to reach. Any 
one teaching singing should understand fully the physi- 
ology of the organ of voice, and then he would appre- 
ciate its delicacy, and not allow screaming or use of the 
voice when fatigued or hoarse. Indeed, screaming or 
shouting at any time is injurious to the voice, as the vocal 
cords cannot be strained or stretched without risk of in- 
jury. Loud talking or loud reading should also be 
avoided, as leading to the same effects. 

The use of tobacco or alcohol is certain to injure the 
throat or larynx. Breathing air loaded with tobacco 
smoke will affect not only the lungs, but the larynx or 
organ of voice, and may produce serious disease of those 
parts. Alcohol will produce huskiness of the voice from 
congestion and inflammation of the larynx and throat, 
and thickening of the vocal cords, which may not be 
curable. 

Proper exercise of the voice will strengthen it, and any 
one by care can increase its clearness and purity of tone. 
Singing, reading, and speaking, if effected with care and 
without straining, will give power to the voice and also 
strengthen the lungs. 

The Voices of Animals. — Birds have very active organs 
for breathing, and it is easy, therefore, for them to sing 
continuously. Some insects produce noises by the rapid 
motion of their wings — the mosquito, for instance, The 



VOICE. 201 

friction against one another of different parts of the 
cricket produces its peculiar shrill noise. The grass- 
hopper's shriek is produced by its rubbing its legs against 
ite wings. In South America a locust exists with a kind 
of drum under its wings, the sound of which can be 
heard a mile or more : if a man had a voice in propor- 
tion it would be heard from one end of the world to the 
other. Insects which fly most rapidly are the noisiest. 



QUESTIONS. 

How is the voice produced ? What are the organs concerned ? 

What is the larynx ? The glottis ? What are the vocal cords ? 

What effect have the muscles on the cords ? 

What parts are absolutely essential to produce voice ? 

What kind of a musical instrument is the larynx ? 

What is the difference in voice of the sexes ? 

What is whispering ? What is whistling ? 

What three kinds of male voice are there ? Of the female voice ? 

What is the range of the singing voice ? 

W^hat is ventriloquism ? Speech ? How was language first formed ? 

On what principle are words like " hissing," " cuckoo," etc. derived ? 

Why is a person born deaf usually dumb also? 

What are some of the rules for taking care of the voice ? 

What effect have alcohol and tobacco on the voice? 

What peculiarities are there in the noises of animals? 



INDEX. 



Absorption, intestinal, 93, 96. 
of chyle, 93, 96. 
of food, 93, 96. 
Adam's apple, 194. 
Air we breathe, 107. 
Air-cells, 104, 107. 
Albumen, 47. 

Albuminoid substances, 47. 
Albuminous substances, 47. 
Alcohol, 57. 

a poison, 58. 

action on the blood-vessels, 135. 
on the bones, 30. 
on the bowels, 58. 
on the circulation, 134. 
on the hearing, 192. 
on the heart, 134. 
on the larynx, 192. 
on the liver, 135. 
on the muscles, 41. 
on the nervous system, 160. 
on the pulse, 135. 
on the respiration, 112. 
on the stomach, 58. 
on the temperature, 143. 
on the vision, 186. 
on the voice, 200. 
as a drink, 56. 
mortality from, 137. 
not a food, 57. 
Alcoholic drinks. See Alcohol. 
Alcoholism, 161. 
Anatomy, definition of, 12. 
Animal food, 50. 
heat, 140. 

action of alcohol on, 143. 

of tobacco on, 144. 
hygiene of, 141. 
Animals and vegetables, differences 

between, 11. 
Anterior chamber of eye, 179. 
Anvil of ear, 190. 
Aorta, 125. 

Appendix of caecum, 90. 
Appetite, 62. 
Aqueous humor, 179. 



Arbor vitae, 151. 
Arterial blood, 101. 
Arteries, 101, 120, 125. 
Auditory canal or tube, 188. 
Auricle of heart, 120. 

Ball of the eye, 176. 

Bathing, 175. 

Beat of heart, 122. 

Bile, 90, 92. 

Birds, circulation, etc., in. See Cir 

culation, etc. 
Birds as food, 50. 
Blind spot of retina, 183. 
Blood, 130. 

arterial, 101. 

circulation of, 117. 

coagulation of, 133. 

crystals of, 132. 

matters secreted from, 137. 

quantity of, 125. 

venous, 101. 
Blood-corpuscles, 108, 130. 
Blood-globules, 108, 130. 
Blood-vessels, 16. 
Body, divisions of, 12. 
Bolting of food, 75. 
Bones, 18. 

effects of alcohol on, 30. 

hygiene of, 29. 

structure of, 18. 
Bones and joints, 18. 
Bowels. See Intestines. 
Brain, 147, 148, 158. 

convolutions of, 150. 

hemispheres of, 151. 

size and weight of, 149. 
Bread, 53. 
Breathing, act of, 104. 

acts, 108. See Respiration. 
Bronchial tubes, 103. 
Butter, 52. 
Buttermilk, 52. 

Capillaries, 128. 
Cartilage, 25. 

203 



204 



INDEX. 



Cartilages of joints, 25. 

of larynx, 195. 
Casein, 47. 
Cells, 137. 

Cerebellum, 148, 151, 158. 
Cerebro-spinal system, 146, 147. 

nerves, 146, 147. 
Cerebrum, 147, 148, 158. 
Ceruminous glands, 189. 
Cheese as food, 52. 
Chest, 101. 

bones of, 22. 

contents of, 101. 

sounds of, 106. 
Chloral, action of, 163. 
Choroid coat, 179, 180. 
Chyle, 93, 96. 

absorption of, 93, 96. 
Chyle-bearing vessels, 96. 
Circulation of the blood, 117. 

action of alcohol on, 134. 
of narcotics on, 137. 
of tobacco on, 136. 

course of, 123. 

greater, 121. 

hygiene of, 134. 

in animals, 128. 

lesser, 121. 

pulmonic, 121. 

systemic, 121. 

velocity of, 125. 
Clot of blood, 133. 
Clothing, 142, 174. 
Coagulation of blood, 133. 
Cochlea, 189. 
Coffee, action of, 59. 
Cold-blooded animals, 140. 
Color-blindness, 183. 
Colors, perception of, 183. 
Columns of spinal cord, 154. 
Contractility of muscles, 33. 
Convolutions of brain, 150. 
Cooking of food, 54. 
Cords, vocal, 194. 
Cornea, 179, 180. 
Corpuscles of blood, 108, 130. 

white, 130. 
Coughing, physiology of, 108. 
Cream as food, 51. 
Crystalline lens, 179, 181. 
Cutis, 171. 

Deglutition, 72. 
Dentine, 65. 
Derma, 171. 



Dextrin, 71. 

Diaphragm, 76, 101, 105. 
Diet. See Food. 
Digestibility of food, 87. 
Digestion, 43. 

changes in food in, 85. 

effect of alcohol on, 57. 
of opium on, 59. 
of tobacco on, 5«. 

hygiene of, 60, 63. 

in animals, 80. 

in the bowels, 76, 88. 

in the intestines, 76, 88 c 

in the mouth, 65. 

in the stomach, 76, 84, 

organs of, 64. 

process of, 75. 
Dislocations, 28. 
Divisions of the body, 12. 
Dreaming, 159. 
Drinks, 55. 

alcoholic, 56. 
Drum of ear, 1S9. 

Ear, 188. 

bones of, 190. 

outer, 1SS. 

inner, 189. 

middle, 189. 
Ear-wax, 190. 
Eating, hints about, 63. 
Eggs, 52. 
Emulsion, 91. 
Enamel of teeth, 65. 
Epidermis, 171. 
Epiglottis, 75. 
Eustachian tube, 189. 
Exercise, muscular, 38. 
Expiration, 104. 
Extremities, lower, 14, 22. 

upper, 14, 22. 
Eye, 176. 

accommodation of, 181. 

coats of, 179. 

color of, 180. 

compound, 184. 

effect of alcohol on, 186. 
of tobacco on, 186. 

far-sighted, 181. 

globe of, 176. 

hygiene of, 184. 

in animals, 183. 

protection of, 177. 

short-sighted, 181. 

transparent parts of, 179. 



INDEX. 



205 



Eyeball, 176. 

muscles of, ISO. 
Eyelashes, ITS. 
Eyelids, 178. 

Face, 13. 

Far sight, 182. 

Fats, 47. 

Ferments, action of, 53. 

Fibrils, muscular, 32. 

Fibrin, 47, 133. 

Fifth pair of nerves, 154. 

Fish as food, 50. 

Fishes, circulation, etc., in. See Ci) 

dilution, etc. 
Flesh, 16, 32. 
Flour as food, 45. 
Fluids at meals, 87. 

thin, digestion of, 86. 
Food, absorption of, 93. 

animal, 50. 

bolting of, 75. 

changes in, in digestion, 86. 

cooking of, 54. 

digestibility of, 87. 

of man, 44. 

quantity of, 60. 

swallowing of, 72. 

variety of, 49. 

vegetable, 53. 
Fruits, 54. 

Gall-bladder, 92. 
Ganglions of brain, 151. 

of nerves, 152. 

of sympathetic nerve, 152. 
Gastric juice, 78. 
Gills of fishes, 114. 
Glands, 138. 

ceruminous, 189. 

lachrymal, 179. 

lymphatic, 95. 

salivary, 71. 

sebaceous, 172. 
Glassy humor of eye, 179. 
Globe of the eye, 176. 
Glottis, 195. 
Grape-sugar, 71. 
Gullet, 72. 
Gums as food, 46. 

Hair, 172. 
Hammer of ear, 190. 
Hand, 173. 
Head, 13. 



Hearing, action of alcohol on, 192. 
of tobacco on, 192. 

hygiene of, 191. 

in animals, 191. 

nerve of, 189. 

organ of, 188. 

sense of, 188. 

voice and, 198. 
Heart, 118. 

action of alcohol on, 134. 
of narcotics on, 137. 
of tobacco on, 136. 

beat of, 122. 

cavities of, 119. 

left, 120. 

movements of, 122. 

right, 119. 

sounds of, 123. 

valves of, 122. 

work of, 124. 
Heat, animal, 140. 
Hemispheres of brain, 151. 
Hunger, 62. 
Hygiene defined, 10. 

of animal heat, 141. 

of the bones, 29. 

of the circulation, 134. 

of the digestion, 60, 63. 

of the eyes, 184. 

of the hearing, 191. 

of the muscles, 38. 

of the respiration, 110. 

of the skin, 174. 

Impulse of heart, 122. 
Indian hemp, action of, 163. 
Insects, circulation, etc., in. See 

Circulation, etc. 
Inspiration, 104. 
Intestinal juices, 90. 
Intestines, action of alcohol on, 58. 

digestion in, 88. 

of other animals, 90. 
Iris, 180. 

Iron in the body, 46. 
Ivory of the teeth, 65. 

Joints, 18, 23. 
Juice, gastric, 78. 
intestinal, 90. 

Labyrinth, 189. 

bony, 189. 

membranous, 189. 
Lachrymal gland, 177. 



206 



INDEX. 



Lacteals, 94. 
Lake-water, 56. 
Language, formation of, 198. 
Larynx, 103, 194. 

cartilages of, 195. 

muscles of, 195. 
Laughing, physiology of, 108. 
Lens, crystalline, 179, 181. 
Ligaments, 25. 
Light, 180. 

reflection of, 180. 

refraction of, 180. 
Liquor sanguinis, 133. 
Liver, 90, 92. 
Lower extremities, 14. 

bones of, 22. 
Lungs, 101, 102. 

action of alcohol and tobacco 
on, 112, 113. 

capacity of, 107. 
Lymph, 97. 
Lymphatic glands, 95. 
Lymphatics, 96. 

valves in, 97. 

Marrow of bones, 18. 

spinal, 147, 151. 
Medulla oblongata, 148, 158. 
Membrane of drum, 188. 
Milk as food, 45, 51. 
Molar teeth, 68. 
Morphia, action of, 162. 
Mouth in digestion, 65. 
Mouth-watering, 71. 
Movements, muscular, 37. 

nerve-centre controlling, 158. 
Muscles, 16, 32. 

action of, 33. 

action of alcohol on, 41. 
of tobacco on, 41. 

fibres of, 32. 

hygiene of, 38. 

of expression, 40. 

tendon of, 35. 

Nails, 173. 

Narcotics. See Alcohol, Opium, To- 
bacco, etc. 
Nerve-cells, 147. 
Nerve-fibres, 147, 152. 
Nerves, 17, 146, 151. 

cranial, 153. 

functions of, 157. 

pairs of, 152. 

spinal, 154. 



Nerve-sheath, 152. 
Nervous matter, 146. 
Nervous system, 146. 
divisions of, 146. 
effect of alcohol on, 160. 
of chloral on, 163. 
of opium on, 162. 
of tobacco on, 163. 
functions of, 157. 
of animals, 159. 
Nitrogenized food, 48. 
Non-nitrogenized food, 48c 
Nose, 168. 

Odors, 169. 

(Esophagus, 72. 

Oils as food, 48. 

Opium, action of, 59, 162. 

Optic nerve, 177. 

Orbits, 178. 

Oval window, 188. * 

Pancreas, 90. 
Pancreatic juice, 90. 
Panting, 109. 
Papillae of skin, 170. 

of tongue, 165. 

of touch, 170. 
Parotid gland, 72. 
Pelvis, bones of, 22. 
Pepsin, 78. 
Permanent teeth, 66. 
Pharynx, 72. 
Physiology, definition of, 9. 

of man, 9. 

vegetable, 10. 
Pleura, 102. 
Pulmonary arteries, 122. 

veins, 123. 
Pulse, 123. 

action of alcohol on, 135. 
of tobacco on, 136. 
Pulse-writing, 126. 
Pupil, 180. 
Pylorus, 77, 91. 

Rain-water as drink, 56. 

Reflection of light, 180. 

Reflex action of spinal cord, 157. 

Refraction of light, 180. 

Reptiles, circulation, etc. in. See 

Circulation, etc. 
Respiration, 100. 

action of alcohol on, 112. 
of tobacco on, 113. 



I>DEX. 



207 



Respiration, changes in, 101. 

full, 106. 

gentle, 105. 

hygiene of, 110. 

in animals, 113. 

in vegetables, 116. 

obstacles to, 109. 
Respirations, number of, 106. 
Retina, 179, 181. 

image on, 181. 

impression on, 182. 
Ribs, 22, 101. 
River-water as drink, 56. 
Rumination, 81. 
Running, 37. 

Saliva, 71. 
Salts in the body, 45. 
Salivary glands, 71. 
Scent of animals, 169. 
Sclerotic coat, 179. 
Sebaceous glands, 171, 177. 
Secretion, 138. 

organs for, 138. 
Semicircular canals, 189. 
Sensation, 157. 
Senses, 165. 
Serum, 17, 133. 
Sheep, stomach of, 80. 
Short-sight, 181. 
Sight. See Vision. 
Skeleton, 14. 
Skin, 171. 

color cf, 173. 

hygiene of, 174. 

papillse of, 170, 171. 
Skull, 13. 

Sleep, physiology of, 159. 
Smell, how effected, 169. 

in animals, 169. 

nerve of, 168. 

organ of, 168. 
Smelling, 109, 168. 
Socket of eye, 178. 
Sound, 189/191 
Sounds of chest, 106. 

of heart, 123. 
Speech, 198. 
Spinal canal, 20. 

column, 20. 

cord, 149, 151. 

reflex actions of, 157. 

marrow, 147, 151. 
Spine, 20, 29. 
3pring-water as drink, 50. 



Starch as food, 46. 
Stirrup of ear, 190. 
Stomach, 76. 

action of alcohol on, 58. 

of opium and tobacco on, 59, 

blood-vessels of, 78. 

digestion in, 77, 84. 

juices of, 78. 

muscles of, 79. 

of animals, 80. 
Sublingual gland, 72. 
Submaxillary gland, 72. 
Sugar as food, 46. 
Swallowing of food, 72. 
Sweat, 171. 
Sweat-glands, 171 . 
Sympathetic nerve, 146. 

system, 146. 

Taking cold, 143. 
Taste, 165. 

in animals, 167. 

organ of, 165. 

sense of, 165. 
Tea, action of, 59. 
Tears, 177. 
Teeth, 65. 

ivory of, 65. 

milk, 65. 

molar, 68. 

of animals, 68. 

permanent, 66. 

temporary, 65. 

wisdom, 67. 
Temperature of animals, 140. 

action of alcohol on, 143. 
of tobacco on, 144. 

of organs, 141. 
Tendo Achilles, 36. 
Tendons, 35. 
Thirst, 62. 

Thoracic canal or duct, 95. 
Thorax. See Chest. 
Tight-lacing, 111. 

Tobacco, action of, on the circula- 
tion, 136. 

on the digestion, 59. 

on the hearing, 192, 

on the heart, 136. 

on the muscles, 41. 

on the nervous system, 163. 

on the pulse, 136. 

on the respiration, 113. 

on the temperature, 144. 

on the vision, 186. 



208 



INDEX. 



Tobacco, action of, on the voice, 200. 
Tongue, 70, 165. 

muscles of, 165. 

nerves of, 166. 

papillae of, 165. 
Touch, 170. 

in animals, 174. 

organ of, 170. 

papillae of, 170. 
Touch, sensation of, 173, 
Touch-bodies, 170. 
Trachea, 103. 
Trunk, 18. 

bones of, 19. 

Upper extremities, 14. 
bones of, 22. 

Valves of heart, 122. 

mitral, 122. 

of lymphatics, 97. 

of veins, 128. 

semilunar, 122, 125. 

tricuspid, 122. 
Vegetable food, 53. 

physiology, 11. 
Veins, 101, 127. 

valves of, 128. 
Venae cavae, 127. 
Venous blood, 101. 
Ventilation, 110. 
Ventricles of heart, 120. 
Ventriloquism, 198. 
Vertebra, 20. 
Vertebral column, 20. 



Vestibule, 189. 

Villi of intestine, 93. 

Vision, 176. 

effect of alcohol and tobacco on, 
186. 

in animals, 183. 

organ of, 176. 
Vitreous humor, 179. 
Vocal cords, 194. 

inferior or true, 195. 

superior or false, 195. 
Voice, 194. 

and hearing, 198. 

in animals, 200. 

in singing, 197. 

in speaking, 197. 

organ of, 194. 

production of, 195. 

quality of, 196. 

range of, 197. 

Walking, 37. 

Warm-blooded animals, 140. 
Water, varieties of, 56. 
Watery humor of eye, 179. 
Waves of light, 180. 

of sound, 191. 
Well-water as drink, 56. 
Whey, 52. 
Whispering. 196. 
White of the eye, 179. 
Windpipe, 103. 
Wisdom teeth, 67. 

Yellow spot of retina, 183. 



THE EXD. 



